Battery bank issues

[resanford]

Hello all. I am trying to help my nephew figure out what is going on, If anything, with his battery bank system. He recently took over my truck camper. For 10 years I had 2 Duracell golf cat batteries from Sam’s wired for 12 volt that I used to run control panel on fridge, led lights and running TV and dvr through a 1500 watt inverter. I knew one battery was bad so we replaced them with new identical ones. Everything seemed to go ok but it seems that he used the batteries for a couple of weeks and let them get really low and also did not charge them back up for a week or so. So they did not seem to be working right and we took them to Sam’s and they tested bad and were replaced. Since then it seems like the new ones are still discharging way too fast. He had a little 240 watt inverter which was all he needed for the TV and any use of the TV through that one or the original bigger inverter caused a fast drop. Basically, it will go from 80 to 50 percent within an hour. To do a test, we disconnected everything down to bare terminals. He then charged them up (with a small Viking charger from HF) to 12.64. He then disconnected the charger. After 2 hours with no load it was down to 12.44. He then hooked up fridge control panel and his lights which he did not use much. After 12 more hours it was at 12.30.
 
Does this seem normal. If so, could his TV or converters be causing a problem. The batteries are only 1 month old and always have had the proper amount of distilled water in them. If the drop observed is not normal are bad batteries the only possible explanation. He is mostly boondocking and recharging using a Predator 3500 generator and the Viking charger. Is using the generator a problem. Is the charger too weak. His use is different from mine in that I did not boondock near as much. I read somewhere of boondocking and the goal basically being charge up to 80% and use down to 50%. Is this acceptable. Thanks for any help out there. Raleigh.

 

[DLTooley]

Try battery university for basics. The first question that comes to my mind is whether you are getting to full charge.

Lead acid batteries like to be as full as possible.

That final topping off is best not done with a generator as it takes some time.

A small solar panel in combo with a generator works well, small enough and you don’t need a controller. A good controller like a Victron will help educate you on what’s going on.

Solar panels themselves are cheap these days.

 

[B and C]

~12.6 VDC is resting voltage (12 hr no charging or loads) of a fully charged battery. The charger should bring the battery up to ~14.4+/- volts and hold it there until amps going into the battery taper to about 0.5% of the capacity of the batteries.

The batteries are not getting fully charged from your description. Charging from a large generator running a small charger is not efficient. Using the smallest generator that will run a larger charger would be better and backed up by solar for the long (hours) waiting for the battery acceptance amps to taper to 0.5% battery capacity is better yet.

 

[highdesertranger]

What he said^,

Lot's of questions and poor battery maintenance in the Original Post

1. charging the dead battery to 12.64 did not fully charge it. Voltage is a poor indicator of State of Charge(SOC), Specific Gravity is much better.
2. dropping to 12.4 should have been the first clue.
3. the voltage needs to reach 14.4 and held there until bulk charging is done and then held in the 13.8 range until the battery is full
4. Lead acid batteries need to be fully charged to 100% after every cycle. Leaving them sit for even a day at less than 100% is very detrimental to their longevity.
5. Using a generator to charge batteries is very inefficient. You must remember it takes hour and hours to recharge a depleted battery.
6. The charge to 80% and discharge to 50% info you got is wrong.
7. Solar would really help

Highdesertranger

 

[PeterPiper]

I would chime in....but it's already been adequately and thoroughly covered.

What the above said

 

[ldsreliance]

Ditto. Batteries are not being fully charged.

 

[bullfrog]

Just curious, did your camper come with a shore power hookup and a house battery charged with a converter and are you still using those? Most campers do. Plugging in the camper to the 3500 watt generator and running it about 2 to 4 hours first thing in the morning to bulk charge the batteries and then allowing a set of suit case solar panels to top them off and supply power during the day works well for us. If batteries are not fully charged by late afternoon then the generator is run another 2 to 4 hours or until they are fully charged. Most inverters use power even when no other devices are plugged in. You are much better off to replace 120 volt AC devices with 12 volt DC ones or only use 120 volt AC ones when running the generator. We use the generator morning and evening usually anyway to run a microwave, ac or heater. Insuring batteries are fully charged daily and that your battery bank is large enough to not be discharged below 50% by morning works well for us. The suitcase solar is easy as you can just clip the leads to the batteries leads. If you are close to SanTan solar with their cheap panels you could keep them charged even better with a permanent 250 watt system but the suit case system has been plenty to top off batteries in sunny Arizona.

 

[jonyjoe303]

If you have the 190ah duracell 6 volt batteries, they would take several days to fully charge with one of the small 4 amp harbor freight chargers. If you had a 40 amp charger, it will still take about 4 hours to reach 80 percent, and then when it reaches 80 percent the amps the battery will accept starts to drop, it will still take maybe another 4 hours to fully charge.
Right now more power is being used then is being replaced. The harbor freight charger is too underpowered, I read the manual for the harbor freight charger it doesnt mention what voltages it charges too, but at 4 amps its just barely trickle charging such large batteries.

 

[PeterPiper]

Yeah, he needs  25Amps for almost 8 hours if at 0 SOC

Could go with 20Amps for 10 hours.

10amps 19 hours.

But 4 amps is about 50 hours

 

[jasper]

A little more info on HDR's tip #1.  The link below is to a slightly crude, but easiest for most people to use specific gravity battery tester. At the bottom of the page are other type testers available.

https://www.amazon.com/Thexton-THE1...t=&hvlocphy=9009541&hvtargid=pla-572414163497