Battery drain

Question

I have 2 interstate batteries SRM 24 deep cycle batteries. Have the VictronConnect bmv712 battery monitor.  Had to leave our camper sit for 4 days without charging and drew batteries down to 11.6volts. I’m still trying to understand the battery monitor, but it said we had over 5 days to discharge. Is that complete discharge or to 50% like many recommend you not go below?  Also, those 1 year old batteries seem to be shot now. Can charge them back up to 13 volts (took them out and put them on a 15 amp charger) but by morning they are down to 11.8 and we use very little in our camper. Led lights. The water pump a little. According to monitor only draining 1.2amp an hour.I picked up some Duracell sli27 MDC series.  Charged them up on a stand alone charger and put them in today  I think my new batteries have 90 amp hours each so I set battery capacity to 180. Is that correct?

lwiddis · Answer

“Had to leave our camper sit for 4 days without charging...”

No, you didn’t! My TT charges fully almost everyday...solar...big solar system for when I’m camping, small solar system for covered storage. Next, did you “cut off” all the parasitic loads? While you could have removed the cables from the battery, a kill switch is easier.

ca_traveler · Answer

For a battery at rest 12.1V is 50% discharged. Discharged batteries should be bulk charged at 14.8V then absorb charged (charging amps are dropping) then float charged at 13.6V. Do you have a good 3 stage charger?

Your Marine Deep Cycle battery is basically a starting battery and not a true deep cycle battery. Deep cycle batteries are the gold standard for RV house batteries.

Your 1.2A draws means 1.2A*24 hrs * 4 days = 115Ah. Your batteries are about 75Ah so 115/(75*2) = 77% discharged. That's about 11.7V and close to your 11.8V.

rtreptow7 · Answer

Are the Duracell deep cycle batteries?  They say deep cycle in the case? I read somewhere that they were made by Deka which is a good company?

laknox · Answer

rtreptow7 wrote:Are the Duracell deep cycle batteries?  They say deep cycle in the case? I read somewhere that they were made by Deka which is a good company?There are very few 12v true deep cycle batteries out there and they are expensive.  Most people use 2 6v golf cart batteries, available at Costco or Sam's, for "light" boondocking.  With 200w, or more, of solar, you're good just about indefinitely.  Hard core 'dockers might go with 4 batteries or go whole hog and use Trojan T-105s.  One guy posted pics here of his battery bank that was 6 2v batteries.  He had something like 400 or 500w of solar.  :B  Then there's lithium...Lyle

rtreptow7 · Answer

Also I have the stock WFCO 9865 in my rv but just ordered a boondocker 1275 4 stage that was recommended. I was trying to bring the interstate batteries back to life with an external 3 stage 15 amp charger but it didn’t seem to help. With the current wfco onboard converter I never saw the amps get up to 14+ when charging a really low battery while looking at my VictronConnect monitor.

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Battery drain

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