slow charging Flooded vs AGM batteries - Page 1
Forum section: electronics / beginners

author: pcm81
author_rank: Regular Contributor
timestamp: December 31, 2023, 07:19:18 pm
content: Occasionally, like every 6 months, I like to top off my car battery. I have:https://www.walmart.com/ip/EverStart-Maxx-Lead-Acid-Automotive-Battery-Group-Size-51R-12-Volt-500-CCA/28275660in my civic.I have the Battery minder 2012 as well as the AGM version of it. Currently the non-AGM version is being used by a friend.Since the 2A charging current is so much lower than battery capacity, does it really matter whether i use regular or the AGM version of the charger for topping off and desulphating my battery? I have in the past just topped it off with current + voltage limited power supply, but i like the battery minder for pulsed desulphation routine. I believe my battery is just regular VRLA, not an AGM.

author: bdunham7
author_rank: Super Contributor
timestamp: December 31, 2023, 07:59:12 pm
content: That battery is neither VRLA or AGM, it's just a vented, flooded calcium-enhanced LA battery. It can take your 2A until the cows come home because the calcium feature helps it reabsorb the gases that are produced so you don't lose much water to electrolyis. You can add water if needed as well, but you usually don't need to and if those batteries do get low on fluid, they generally are on the way out anyway. So charge away.

author: pcm81
author_rank: Regular Contributor
timestamp: December 31, 2023, 08:36:51 pm
content: Quote from: bdunham7 on December 31, 2023, 07:59:12 pmKind of makes sense and matches what i thought. The only real difference that i could find in spec sheets for the AGM vs non-AGM battery minder charger is the cutoff current at which they switch from adsorption phase to float phase. 0.5A for non-AGM version vs 0.1A for AGM version. I guess the worst thing that could happen is it will stay in adsorption mode rather than going to pulsed trickle/desulphating mode. While the other way around, AGM battery on non-AGM charger would go into trickle mode too early and not fully charge.Am i missing something else?Trying to learn the finer details, not limited to these chargers, while exploring these specific charges.

author: Gregg
author_rank: Super Contributor
timestamp: December 31, 2023, 10:11:28 pm
content: All varieties of lead acid batteries like to have a continuous float charge of approximately 2.25 volts per cell with slight variations for temperature and exact chemistry.They like to have a quick recharge immediately after a discharge cycle. Also occasional equalize charge of approximately 2.35 to 2.4 volts per cell will help longevity.

author: floobydust
author_rank: Super Contributor
timestamp: December 31, 2023, 11:02:33 pm
content: Modern cars with ECU-controlled alternators do undercharge their batteries, the goal is around 80% SOC so you can do regen during decel going down a hill etc. and get a bit higher mileage. It's not my idea, and the coulomb counter approach does fail as batteries get older and have lower charge efficiency. Some cars have current-sensors on the battery.I regularly top up with a 2A charger, it peaks at 14.6V then floats at 13.8V, with my flooded Panasonic battery. Works great, cells balanced now and no significant water loss. For years I had one cell losing a lot of water compared to the others. Toyota is around 13.4V only and poorly temp compensated.AGM manufacturers do not recommend equalization charging- but I'll do it because no battery has perfectly matched cells. With age you will get a weaker cell and it never gets a chance to catch up otherwise. Just don't do it hard as you don't have that much extra water there.

author: BlackICE
author_rank: Regular Contributor
timestamp: January 01, 2024, 12:09:12 am
content: My limited experience with flooded cell lead acid batteries is that they can be "rejuvenated" by over charging limiting current to < 0.05 of the AH capacity and voltage >=15V or so if you keep the water level up. I guessing that overcharging help re-balance the cells. I tried this also with "sealed" AGM batteries with limited success by breaking the seals and rewetting the mats with water.Under charging to increase gas mileage is not going to help the batteries lifespan. Any lead sulfate that forms and shakes off the plates from the car's vibration is forever lost.

author: pcm81
author_rank: Regular Contributor
timestamp: January 01, 2024, 01:29:00 am
content: Quote from: BlackICE on January 01, 2024, 12:09:12 amThis matches my experience as well. I am usually able to rewet and restore flooded but not agm batteries.Interesting to note hat the AGM charger connected to my regular wet battery did sense end of charge and switched to trickle mode. Based on the spec sheet it switches at lower current than the regular charger, so i was half expecting for it top stay in top-off mode rather than correctly switch to trickle.

author: BlackICE
author_rank: Regular Contributor
timestamp: January 01, 2024, 01:38:24 am
content: I use a bench power supply to charge them using the current limit and set the voltage to 15.5v. Warning if you forget to turn on the power supply 1st it could fry. Same thing if the power blackout happens while charging. To be safe use a series diode and compensate for the voltage drop.How do I know I burned out the output diodes on my power supply when I connected the lead before turning the power supply on. I was lucky to fix it by replacing 2 diodes.

author: floobydust
author_rank: Super Contributor
timestamp: January 01, 2024, 08:31:28 pm
content: Also note a car will "do things" with key off. Canister purge test, cycle the fuel pump etc. which confuses "smart" chargers because everything looked all happy float charging- and a load gets switched on and voltage sags. Firmware makes mistakes, from either doing nothing or re-starting the charge sequence over and over. It's more of an issue for RV's and motorhomes (caravan) where they are on a charger and lighting/pump etc. loads get switched on and off, a stupid charger can let the battery actually get drained.Honda Civic uses the smallest car battery available, that Group 51. I'm surprised they last that long, when I owned one.