sailracer

This week the mower was still at 100% after sitting for a week on the charger. While I wouldn't call this conclusive, it is a datapoint supporting the idea that the 70% reading problem could be related to a bad battery self-discharging faster than good batteries. I'll keep checking as the time between mowings increases later in the summer. Update- one week later and the 70% problem returned. I did notice that the finishing % when I was done with my lawn was the same as the week before when it started from 100%, so it seems like it must just be a voltage variance sensitivity reading when the batteries are fully charged and doesn't really reflect 30% less energy in the batteries.

So far I haven't had any issue with charging. The mixed pack charged back to 100% (52.9V) overnight. I'll check later this week to see if it has the self discharge problem where it drops a volt and reports 70% when on the charger for a week or more. The MM battery ordered from Amazon came mostly charged I think. It read 13V when it arrived. I put it on a trickle charger for 24 hours before installing it in the mower with the other fully charged batteries.

I'll add my conclusions after experimenting with my batteries and tester. For a typical car battery for starting an engine, CCA is important. The batteries are designed for supplying large amps over a short period of time. They are also not meant to be deep discharged and need to be fully charged to operate effectively, so car starting batteries are tested at full charge. Deep cycle batteries aren't designed for outputting large amounts of current over a short time but instead are designed to output a working current for a long period of time and be able to sustain that current as the battery discharges. Deep cycle batteries can still generate a large current in short time, but the amount of that current is dependent on the state of charge and may not be a good indicator of battery health, so any tester that only tests for a short period of time may not be able to detect a problem with a deep cycle battery, particularly if it is a problem that requires heat build up in a battery to show up. The small, consumer load testers like the one I tried, are designed for measuring that peak current over a very short period of time and the tester determines health by comparing that current to the rated CCA of the battery. The much bigger commercial load testers are likely using a test method with better heat dissipation so they can test for a longer period of time and can observe voltage drop over that time period. They can safely apply a load for many seconds to see if the battery charge can hold up over that longer period of time. That seems more likely to find a problem with a deep cycle battery, but still may not be sufficient. If the load current is high, it isn't testing the deep cycle battery the way it was intended to be used. If the load current is lower, it may take a long time to determine its state of health. Looking at the battery discharge graph I posted earlier, using highest current discharge they show (depletes the battery in 30 minutes, which extrapolating from tables in the datasheet suggests the current is around 85A) it takes 8 minutes of load at 85A for the voltage to drop from 11.9V to 11.6V. To test that, the load tester would have to dissipate >1000W for 8 minutes. That's a big toaster worth of heat! The measured CCA with my small meter showed approximately 40A of difference between the 4 batteries in my mower when fully charged. The battery that ended up being bad was actually one of the ones with a high CCA measured by the charger. With the blades running (drawing an approximately constant load I estimate to be around 30A) all of the batteries had a very similar measured voltage when all were fully charged. Even the bad battery was able to output the required current without showing an abnormal voltage drop when fully charged. Depending on how much current a battery load tester draws and for how long, it may not detect a problem with this battery when fully charged. Once the deep cycle batteries had been discharged more, things started to change. The consumer battery tester showed the CCA of all 4 batteries dropped. The bad battery dropped more than the others, but was still putting out 360 CCA when mostly discharged. The others were at 400 to 430. That alone can't diagnose the problem, but now the voltage on the bad battery was reading only ~10.5V while under load whereas the good batteries were still at 12.3V. Another clue- the bad battery had a spot on the case that felt hot to the touch after discharging for an hour. I don't know that any load tester can run a battery long enough for it to heat up internally like that. Maybe there is some clue in the voltage/current before the battery heats up or at much higher currents maybe it shows up quickly. Maybe someday if I get around to it, I will take my bad battery to a shop for testing to see what they say. In terms of power, the bad battery is putting out a little bit less than the good batteries. Since they are wired in series, the current through them is the same, only the voltage differs, so the bad battery is putting out about 15% less power than the good ones based on the voltage difference. The Ryobi battery management seems to key off voltage for battery state of charge, however, and thinks that this much drop in voltage means the pack as a whole is more discharged than it actually is. The battery still seems to have the charge in it, but is not capable of outputting it at the current required which causes the voltage to drop. If the bad battery sits and cools down, the voltage comes back in line with the other batteries and the Ryobi gauge goes from reading 5% up to 40% and is happy again and the mower can run for longer. So, whatever is wrong with my battery internally, it seems marginal right now (but getting worse over time) and only shows itself when the battery has been running long enough to build up some heat internally. For those trying to determine if it is time to replace all of your batteries and want to diagnose it yourself, I would say do an extended load test to determine if there is one battery in particular causing your pack voltage to drop as the batteries discharge or if all of your batteries are dropping the same and have worn out evenly.

I put in the new MightyMax 75Ah battery to replace my original battery that I concluded was bad and it seems to be working perfectly. So far I don't see any evidence of a problem mixing Leoch and MightyMax. The terminal positions are slightly different on the MightyMax but the battery jumpers still reach them easily, and it has a fabric lifting strap instead of plastic handles. I mowed last night and finished with 35% battery remaining instead of either flashing 5% or blades shutting off before I was done, so it looks like it was another premature Leoch battery failure and replacing it resolved the problem. Here's a picture. I discovered this morning I forgot to put the plastic battery covers back on. Is it worth taking everything apart again to put them back on or should I just run without them until the next time I need to service a battery?

It seems a little odd that the voltage dropoff was only occurring on my battery once it was discharged well below 100%. At full charge it looked like everything was fine, even under load. I don't know enough about battery design to understand what type of problem may cause that behavior. It's like it's OK at sprinting but has no endurance whereas a good battery can do both I ordered one of the MightyMax batteries as a replacement. It will be interesting to see if the 70% full charge problem goes away after replacing the bad battery. If it does, that might be an early indicator of a battery with a weak cell.

I don't know, I haven't looked around. I don't really want to, even if they do the testing for free because then I would feel kind of obligated to get a replacement battery through them. There's also the possibility they don't know what they are doing with deep cycle batteries vs. car starting batteries and they tell me I have to replace all 4 of my batteries. I'd rather do things myself to learn and understand what is going on. Speaking of which, I just ran another experiment. I turned the battery pack around so I could connect it to the mower while hanging out the back where I could measure it. I had my wife engage the blades while I measured the voltage on each battery. With the pack at 100%, each battery measured about 12.25V under load with the blades running. I ran the blades longer until the pack reported 70% charge, and all the packs still read around 12.25V. I continued running the blades until the indicator read 25%, then turned it off and measured the voltages. Packs 1-3 were all around 12.3 to 12.4V but pack 4 was at 10.2V! That battery also had a hot spot on the case in one area. None of the other batteries had any warm spots. The voltage on that battery gradually crept back up once the load was stopped. So, that must be the one that is causing the problems. What's more, it shows the CCA from the test above is useless for determining the health of a deep cycle battery when it is at 100%. I retested all 4 batteries with the tester. All of them were lower than when charged to 100%, but pack 4 was down to 339A. Pack 1 and 2 were about 405 and pack 3 was at 445.

Here's what I found with the battery tester I linked above. It appears to measure the CCA and determine the health of the battery based solely on that. It uses the number you give it for a target CCA to tell you the battery state of health. I'm not sure what the CCA should be for a good Leoch 75Ah battery since that isn't how deep cycle batteries are spec'd. Does anyone know what a good vs. bad battery will typically read for CCA? All 4 of my batteries measured between 13.06 and 13.12 V when fully charged and removed from the system. I got the following for CCA on each Batt 1: 466A Batt 2: 474A Batt 3: 536A Batt 4: 527A This would seem to suggest two of the batteries (the two towards the back of the mower) are weaker. Does it mean they are bad, though?

That's weird the maintenance behavior changed. Either way, it sounds like the charger doesn't trickle charge for maintenance but instead looks for a threshold to turn on and top up the batteries at a higher current. That could explain the 70% problem many people have. Or maybe a battery with a bad cell causes the pack voltage to drop from 100% reading to 70% reading while on the charger within a week. Maybe everyone with the 70% problem and the batteries still under warranty should have them tested before warranty runs out and they start degrading faster! Has anyone had luck testing these batteries with a basic battery tester? Something like this: Amazon.com: LNEX Car Battery Tester , 2.8'' LCD Color Screen, 100-2000CCA Fast Accurate 12V Battery Load Tester, Cranking and Charging System Digital Battery Analyzer for Car Truck Motorcycle ATV SUV Boat Yacht : Automotive Edit: Found this tester for $20 and bought it. Should be here tomorrow- I'll report back on how it works. Amazon.com: KINGBOLEN BM550 6V 12V 24V Car Battery Tester, 100-2000 CCA Voltage Tester 2Ah-220Ah Internal Resistance Tester Accurate Digital Auto Battery Analyzer for Cars Trucks SUV ATV Boats Motorcycles Vehicle : Automotive

Hi all- I just joined these forums for this thread. I have a 75aH Zero Turn that is 2 years old with 39 hours on it that can no longer finish mowing my ~1.2 acre yard on a single charge. Since it was new, it often had the 70% full charge problem. I've investigated further after reading this thread. It appears that the charger fully charges the batteries to 100%, then turns off and never charges or trickle charges them again, so that after a week of sitting before the next mow, the batteries have self discharged a little and the voltage is down. I checked things with a volt meter this week to confirm. After sitting for a week on the charger, I turned the mower on and it read 70% and voltage measured 51.6V. I then plugged it back in for a couple hours and checked again. This time it was at 100% and measured 52.4V. I then charged overnight and it was at 100% / 51.3V. A week of sitting on the charger later- back to 70% <52V. It appears the charger doesn't keep the batteries topped up. The Winter behavior I saw seems to suggest it is never trickle charging, not that it just didn't a low enough threshold to start trickle charging. When I turned the mower on this Spring after sitting for 3 months (on the charger in a garage that never gets below 40 degrees) it read 40%. It seems to me charger isn't behaving the way it is supposed to since Ryobi recommends keeping it connected. As for not being able to complete a full mow, after about 40 minutes when the blades shut off now, if I let the mower sit for 20 minutes, the reading goes from 5% to 40%. Does this give any clue if maybe it is just a single battery going bad or is it meaningless? What kind of load tester is needed for these deep cycle batteries? It looks like most battery testers apply a fixed load for a very short amount of time and measure the voltage drop over that time. Can those meters reliably test a deep cycle? It seems like their current load could be too high if designed for car stating type batteries and might not give accurate results. Finally, based on the number of premature failures here it seems like Ryobi should be doing something. I feel like I was ripped off if I need to replace my batteries after 39 hours of use. Even at $5 a gallon for gas, the battery cost alone is more than double what my gas mower would have cost me over the same time. Thats not even counting the cost of electricity or how expensive the mower was. Jamis- you've been providing lots of great info here, but I need to question your statement about Ryobi only allowing 30% discharge on these. Where did that info come from? I see this chart from the Leoch datasheet which suggests that a battery only discharged 30% will still have half its capacity left after ~1200 discharge cycles. It also shows that a fully discharged battery will be at half capacity after less than 300 discharge cycles. I expect Ryobi is allowing much closer to 100% discharge than 30%. Based on your previous post referencing 34V, I'm guessing you correlated a 30% discharge with a 30% drop in voltage? I would argue that a 30% discharge is referring to the energy in the battery. That is, a 30% discharge means you used 30Ah out of the 100Ah available. The voltage does not go down linearly with the energy as this second chart from the battery datasheet shows: Based on this chart I expect the dashed line represents 100% discharge. When my blades shut off after 40 minutes of mowing, my pack voltage is around ~38V which would suggest from this chart that the battery is pretty much fully discharged.