Battery help, One bad one in my string.

BrluxBrlux Solar Expert Posts: 73 ✭✭✭
I have a 48V system running 8 T-105's in series. They are about 30 months old and recently I noticed one of my T-105s is only sitting at around 3V while discharging over night while all others are around 6V. My question is could/should I replace the one bad battery with a new one or is it only a short mater of time before the rest of them are on their way out?

I would like to replace my 8 battery string wit L-16RE's but that is a financial commitment that I am not sure I am ready for any time soon.



  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery help, One bad one in my string.

    Change out the one battery before it causes harm to the rest.

    Normally you'll hear the advice "don't mix batteries of different ages" and 30 months is definitely different ages. But risking "dragging down" one new battery over definitely "dragging down" seven ...

    You don't know how long it's been bad, either. Could be only a few days so the rest might not be stressed.

    One T105 is certainly cheaper than a bank of L16's! (Which may need additional PV to keep charged, depending on the size of your existing array. It's 225 Amp hours vs. 320/390.)
  • BB.BB. Super Moderators, Administrators Posts: 30,511 admin
    Re: Battery help, One bad one in my string.

    With one bad battery in the string--it will likely take the others out too.

    You are down to either replacing the existing battery (new or used) or replacing the whole string. I would hope that the others are OK.

    Do you have any reason why the one battery is having problems (did you take the whole bank dead at any time, expose the plates, use well water for refilling, etc.)... Trying to figure out if this was something that damaged the whole battery bank or just a single random battery failure.

    You might try talking with your battery supplier and see if they can help you (diagnose the battery, possible warranty help, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BrluxBrlux Solar Expert Posts: 73 ✭✭✭
    Re: Battery help, One bad one in my string.

    I would guess it has been going on for a week or two. That one particular battery had a corrosion build up on one of it's terminals a year or so ago, it did get very hot under load before I noticed and cleaned it. I am thinking of getting one lower priced golf cart battery like the ones form Costco $75 to replace this one versed a new T-105 $150. What do you all think of this idea? I don't want to risk to much as the others could go out at any time.

    I always fill with distilled and have never exposed the plates.

    I think I have only had the low battery warning buzzer on my Exeltech XP-1100 go off once with this battery bank and they usually are 48V or higher so I don't think I have been very rough on them. What kind of service life have others seen out of their T-105 batteries?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery help, One bad one in my string.

    go for replacing the battery with a cheaper one from costco and in the meantime you can put a few $ away every month to your future l16 battery bank.
    odds are there was something amiss with the battery from the getgo, but took its time to eventually show up to kill the battery. bottom line is, they are sometimes just bad batteries. you probably still have 7 more good ones in the string with hopefully a few more years to their lifespan.
  • BrluxBrlux Solar Expert Posts: 73 ✭✭✭
    Re: Battery help, One bad one in my string.

    So out of curiosity what are the expected or experienced service life for T-105s in an RE system?

    I previously had 16 US2200 golf cart batteries in a 8s 2p configuration and they only lasted me about 30 months and I was very gentle on them.

    For those who are interested I typically see solar charge currents around 14A.

    I also run a 12V system which has 2 T-105s on it and they are roughly the same age as the ones on my 48V system. Should I put the new cheep Costco battery on the 48V system or on the 12V system and move one of my 12V t-105s to the 48V system?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery help, One bad one in my string.

    I'd expect five years minimum out of a set of Trojan T105's. Similar batteries should perform as well.
    I think Tony holds a record with nearly 10 years usage for some of these.

    Keep in mind Trojan recommends a 10% recharge rate - that's 22.5 Amps for a single set (two 6V in parallel for 12V system). Even so, 14 Amps should be sufficient. But not for a parallel set (450 Amp hours).

    Maybe time to examine the whole system and see if something's a little out-of-balance?
  • moorsbmoorsb Solar Expert Posts: 38
    Re: Battery help, One bad one in my string.

    The life of the T105 is dependant upon how low do you let them get. Trojan says if you let them discharge 20% then they should last 10 yrs. If you let them discharge 50% then probably 4 yrs. How low have you been letting them get?

    Is there a device that will let you set alarm points for those levels?
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Battery help, One bad one in my string.

    Get a Bogart Trimetric battery meter so you REALLY know how much you are putting in, and then taking out on a regular basis. With out a good battery meter, you are really just guessing. My hunch is that if you are only getting 30 months out of a set you are either regularly undercharging, or over drawing or a combination of both.

    I have a pair of T-105 that are now in year 11. They were used lightly, full time for seven years, and now have been on standby float service, powering a few reading lights and a fridge control in a remote cabin for a few months per year.

    My current set is in year 3 and seem to be as new.


    As a PS, consider this when you go to replace your battery bank.

    When we built our new house we had been running a used set of 4 L-16s. We did an AH calc of our expected loads, and realized that we would seldom draw 4-t-105s more than 10-15% on a daily basis, or ~5% of 4 L-16s. We then did a cost calc, and determined that if the t-105s last 5 years, and the L-16s 7 years, the T-105 would be cheaper net/net after 5-7 years. Any life after 5 years was a bonus. The result was we went with the smaller, cheaper T-105s instead of the larger, more expensive L-16s. I will report in again after year five! (Of course if the L-16 last 10 years or more, then they might have proved to be cheaper, but then there is the cost of the money to consider. The bottom line is, bigger isn't always better. Having a balance between the charging capacity, the loads etc seems to be the best determinant for longevity).

Sign In or Register to comment.