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Ron_Nielson's avatar
Ron_Nielson
Explorer
Aug 23, 2013

New Batteries Don't Last Long

Posting this question/problem for a friend so I only have the information he sent me. He has a KZ 26TT about 2006 vintage, now camping in Colorado with no electrical supply,and uses a Honda 2000-I generator to do the charging. There is just himself so no group of kids using the trailer. He is an experienced RV'er. Here is his question/problem:

I have two new marine batteries which have only been used for 5 weeks. I fully charge both batteries at 25 amps, but they run down after two days to 25%. Batteries really don't do much: charge phone and computer, run water pump, frig electronics, 12 volt stereo, lights (only one at a time). Just minimal electrical usage. I feel like something is consuming my battery power, but just don't know what it could be. So every two days I fully charge the batteries, which takes about 6 hours to charge at 25 amps.

I've tried just one battery at a time, and it will only last 1 day. Each battery functions the same, doesn't appear to be any difference between the batteries. I just feel like they should last much longer. One other thing, I do run a 400 watt invertor to charge the phone and computer, but still those batteries should last longer.

What do you think?

28 Replies

  • Charging seems to be adequate IMO. Time to find out where the power is going.
    Any chance you have a fridge humidity control (12v heater) that is on? Some don't even have a switch.
    Fairly common post: fridge heater

    Do you turn the inverter off when not in use?

    Is the battery voltage dropping to 11.9 or less?
  • If he's been running them down to 25% over and over again they could already have lost capacity. It would help to know the specific type of batteries. "Marine" could mean all sorts of things.
  • Almot's avatar
    Almot
    Explorer III
    Tell him to get a $3 multimeter, do his 6 hours charging, rest battery 24 hours without loads and check the voltage. If it's less than 12.7, then it's not full.

    Laptop + phone + inverter losses + lights + pumps + radio (both playing and standby) + detectors = can be anywhere from 15 to 25 AH, depending on lights. DC circuit of propane fridge will draw another 10-15 AH, could be 20 AH with fancy features like door defroster. Total 25-45 AH a day. What is his "marine battery" - 80 AH? If it's not fully charged at the beginning (I suspect), it will be down to 25% in one day, just like he said. Or if it's 60 Ah and fully charged - it will be down to 25% in a day.
  • Some additional information:

    My batteries are group 29, the biggest marine battery walmart sells. I use a "real" volt meter to determine the voltage. My charger is a good one, as you know, and after 6 hours of charging, it stops charging and indicates the batteries are full. As I watch my charger charge, it starts at 25.7 amps and then gradually lowers its amps down to full charge. Again, checking with my volt meter after full charge, the volt meter registers about 13.06-13.10 volts.

    I'm not just using the trailer charger, I'm using both the trailer charger and a very good charger which tells me battery state. I know the battery is getting 25.7 amps from the charger, plus whatever the trailer's putting out.

    Thanks for the help.
  • yikes! Not really enough information to give any specific guidance. How does he know 25% and where is he getting 25amp charge rate from?

    If I grossly assume the 25% is one light on the OEM meter and his 2006 vintage original converter is rated at 25amps (where he is getting that number) then 6 hours charging is not going to get him anywhere near fully charged. Starting at a very low state of charge with that assumption it could take a couple days to fully recharge unless he has replaced the OEM converter with a smart converter he is forcing into boost.
  • 25 amps won't fully charge two batteries in 6 hours no matter what batteries they are. You're not starting with a full charge.
  • Hi,

    I wonder how he knows it is 25 amps? Is he using the converter to do the charging?
  • Group 24, 27 or 29? Seems fast but not unreasonable.

    To really find out he will need an ammeter to discover the minimum idle draw of the RV.

    25 amps for 6 hours is a good charge but probably not 100%.

    How does he figure 75% discharged? I hope it is not that oem indicator that also shows the tank levels. Need a real voltage reading with minimal load.

    The 12 Volt Side of Life