Battery Charging Methodology

[Dan McMartin]

I've got another question about charging batteries. This one is more big picture. I can't find a satisfactory answer.

Am I harming my batteries to run them between 50% and 80-85%, basically bulk charging them every day, and then charging them to 100% as we drive between camp spots, in RV parks, a long generator run, etc. every few days?

I know absorption charging takes just this side of forever and running a generator for and additional 4-5 hours a days is expensive and annoying. I get the idea that I should either do as I suggest (let them run in the 50-80% charge state for a few days while boonsocking) or charge them to 100% but I shouldn't be partially charging the batteries to like 90% (half way through absorption) as a rule.

Am I wrong? And as a rhetorical side note, why does this have to be so hard?

[twinboat]

I very often run my battery banks between 50% and 80% discharge on my MH and liveaboard boat.

It's my understanding that flooded batteries can tolerate this kind of use better then AGM batteries.

[Dan McMartin]

Originally Posted by twinboat

I very often run my battery banks between 50% and 80% discharge on my MH and liveaboard boat.

It's my understanding that flooded batteries can tolerate this kind of use better then AGM batteries.

Good to know. Solar will eventually make it a moot point to a large extent since I could let the generator bulk charge in the morning and then solar should take the bank up to 100%...ideally anyway.

[computerguy]

Yes you are "damaging" them. The deeper the discharge the more build up on the plates. The large the buidup the less chemical reaction and less output available. I am no expert. Common reference by manufacturers say 50% DOD is a good balance for FLA. I know some how have lived by this rule and their batts are still strong after 6+ years

DOD Deep-cycle battery
100% 150-200 cycles
80% 400-500 cycles
50% 1000+ cycles

You sacrifice cycles for DOD. Just depends how long you want the batts to last IMO

[Dan McMartin]

Originally Posted by computerguy

Yes you are "damaging" them. The deeper the discharge the more build up on the plates. The large the buidup the less chemical reaction and less output available. I am no expert. Common reference by manufacturers say 50% DOD is a good balance for FLA. I know some how have lived by this rule and their batts are still strong after 6+ years

DOD Deep-cycle battery
100% 150-200 cycles
80% 400-500 cycles
50% 1000+ cycles

You sacrifice cycles for DOD. Just depends how long you want the batts to last IMO

I should be clear. My percentages are not DOD but charge state. So when I say use the battery between 50% and 80%, I mean 50% to 20% DOD.

[computerguy]

Originally Posted by Dan McMartin

I should be clear. My percentages are not DOD but charge state. So when I say use the battery between 50% and 80%, I mean 50% to 20% DOD.

You should be good then IMO.
Looks like I was commenting on Twinboats reply.
Equalizing FLA batteries periodically is not a bad thing either. Periodically is open for discussion though. Some say once a month some say once a year. It basically cleans up the plates so there is minimal build up on them. Makes them a smidgen more efficient and last a longer time. Also depends on how often they are cycled, are they left plugged in on float for a month at a time, etc.

[twinboat]

I was trying to say " state of charge " as the OP was stating.

I run between 50% and 20% D.O.D ( Depth of Discharge ), while off grid, not the lower 20% to 50% D.O.D

[twinboat]

I was trying to say " state of charge " as the OP was stating.

I run between 50% and 20% D.O.D ( Depth of Discharge ), while off grid, not the deeper 20% to 50% D.O.D

[C.Martin]

Whenever you don't get back to 100%... I believe the sulphate buildup is not forced into solution. Best practice...fully charge each cycle. But, if you are doing it every few days...perhaps that is good enough. You may consider doing an Equalization charge a little more frequently...just to get the sulphate back into solution. You just don't want to go too crazy that you erode the plates.

[Dan McMartin]

Honestly, it's a temporary situation, hopefully. As I said, solar should take care of the problem. Bulk charge off the the generator for a couple of hours and then let the sun take over for absorption. If we end up with enough solar, we can also offset some battery use during those hours.

I'll keep the equalization idea in mind.

I kind of assumed those without solar and rely on generator power when boondocking operate between 20% and 50% DOD what with absorption taking 4 hours or so and then top off every few days one way or another.

And maybe someday we can go lithium and not worry about it at all