Testing an old lead acid. - Page 1
Forum section: electronics / projects

author: paulca
author_rank: Super Contributor
timestamp: April 05, 2023, 07:28:36 pm
content: 100Ah Yuasa Marine "START" battery. 4 years old. Spent almost all of it cycling daily on a 50W solar, maybe 10-20% DoD usually. In winter it got flattened twice to 9V. Every winter it got run to 11.xV before being mains charged. After 3 years it appeared "lazy" so I let it get to 12V, gently took it down to 10.8V over a few days and then slapped it hard with 10A, 15V. CCCV and then cutting to 13.60V for an overnight.At probably 1200 cycles, it's not going to start any boats, lets say.I charged it, for test today, as:14.40V < 1% C (alt 15.00V <1%C for <10min)It was already charged and spent all day at 1 amp CC. Voltage settled around 13.40V complicated by a 5 watt load. I was using 14.40V and a current limit of 1 Amp, with the 5W load. It means the lead acid was consuming about 5-6W That voltage changed only from 13.20V at 9am to 13.40V by 5pm. This should be all happy kittens and fluffy dice, puddin's and rice for a LA, pampering it.Later I dropped the load off and boost charged it at 14.40V with the same bench PSU. Initially it went constant current at 5A, but after a few seconds it came down to 4.xAmps. A few minutes and it came down to 2Amps. Not long after, 1 Amp.Connecting up and using the DC load I measured the voltage without the drop at 14.2V and so pushed the PSU up until the battery measured 14.40V with an unloaded meter. I called it "charged" when the 14.40V current dropped below 1 amp. 1%C.Removing the load at that point and the voltage fell rapidly to 13.0V and continued 10mV a second onward. Settling around 12.88V. I gave it 13.60V and it settled in around 0.55A "quiescent". (Quite disgusting for a Lithium convert).So I added first a 1 amp of load and it dropped to 12.50V immediately. Releasing the load and it recovered back to 12.78V.I set the load up to take the battery down to 12.0V measured load side. Figured it would just "over power" and say "Nope." which it, really, really should have. That's NOT a small battery, that should be capable of melting a 10mm spanner!So engaging the battery discharge in CV mode at 12.0V resulted in 11.4A which rapidly fell (thankfully) to 8.4A within a minute and 5 minutes later was down to 6A.Noting the voltage drop meant the actual voltage (this time measured by the power supply set to CC 0Amp) registered 12.50V.So I tried to equalise that out by lowering the CV to 11.3V Taking a total of a 800mV voltage drop to get 13.5A peak. The hardware in use will not tolerate that beyond a quick test.Recap: Fully charged (90% worst?) it can produce 13.5A above 12.0V. I don't wish or have hardware to test it's short circuit but I did see a 25Amp spike on the data.I put it back to CV 12.0V load side measuring. In the length of time it took me to write this (15 min?) it's down to 3.0Amps with 250mV drop.Capacity so far, 3Ah.Unfortunately, while I am quite curious if it has a gammy cell and the rest over charged .... I do need it to stand in for a while as a buffer battery. I only need 1-3amps tops and I can nearly constantly support it. Just not constantly, hence it's requirement to exist for ... a valiant final life. <sniff>I'm going to "call it" when it can't support 1 Amp at 12.0V.When it's replacement arrives I want to drive it down much deeper to see what the voltage curves do. Might reveal something... then the recycling centre.

author: trobbins
author_rank: Frequent Contributor
timestamp: April 06, 2023, 12:26:15 am
content: Perhaps suggest that unless you can cycle the battery a few times to its specified voltage limits (assuming you have located a manufacturer product sheet and maintenance/service info) then any psuedo testing is a bit nebulous and of no tangible merit. PbAc batteries start to degrade as soon as they are made, and 'flattening' a battery is typically causing permanent and sometimes severe degradation from the very first event.If you want to see if the battery can support some form of limited application, then test to that application (ie with repeated discharge and charge cycles to defined end voltages and with reasonable rates).

author: paulca
author_rank: Super Contributor
timestamp: April 06, 2023, 08:16:56 am
content: Well, when I went to bed I turned it off.It had produced 10Ah and was delivering 1.8Amp at 12V.That's about all I need for the few weeks till it's replacement arrives.As it's a lead acid and it's indoors, it will not be subject to any currents. Charge 3A, discharge < 2A. I don't want any venting or bubbling.

author: tautech
author_rank: Super Contributor
timestamp: April 06, 2023, 08:36:46 am
content: Quote from: paulca on April 05, 2023, 07:28:36 pmIt's completely fucked !That sort of battery probably has a 600A CCA engine start rating therefore only providing 13A sounds the death knell for it.

author: SeanB
author_rank: Super Contributor
timestamp: April 06, 2023, 10:10:00 am
content: Check if there are cell caps under the plastic label, there often are, and you will see most of the cells are dry. But yes it is EOL, though in a pinch you can open the top and fill it with distilled water, getting more life out of it. Should be easily able to supply 100A without dropping below 11.6V if good, that it drooped so much with a low load says it is very dry inside.

author: paulca
author_rank: Super Contributor
timestamp: April 06, 2023, 10:18:23 am
content: Quote from: SeanB on April 06, 2023, 10:10:00 amThere is a cover at the back, however the last time I inspected it, it has plastic welding points, so I expect they don't want you to go in and attempt to fill it. I have seen some people dismantling some "Sealed" "Maintenance free" batteries and they do not make it easy. Dremel may be needed.It does "slosh" if you shake it. So it has some water and it's not full.I'll see if I can open it when it's out of it's retirement job.

author: rstofer
author_rank: Super Contributor
timestamp: April 07, 2023, 02:35:18 pm
content: Starting batteries aren't intended for cycling applications. Look at the weight difference between a starting battery and a deep cycling battery.'No Maintenance' batteries are, by design, non-maintainable. You generally can't get to inter-cell busing or even measure the pH. There usually isn't even a way to add water. They do, however, have a price advantage. That's because they don't have robust lead plates.https://batteryuniversity.com/article/bu-804-how-to-prolong-lead-acid-batteries