Trying to Determine if Battery is Dying

mjp24cohomjp24coho Posts: 104Solar Expert ✭✭✭
I’m trying to figure out of my forklift battery in my offgrid system is dying. I have ~4 years on my 800 A/hr 24v forklift battery - it’s been working great over the years, but suffered a hard winter a year ago when my panels were covered with snow and I couldn’t get there to my cabin for a few weeks to clean the panels off. The battery can handle minor loads fine now, but seems to be struggling when running my washing machine (washer kept restarting). I tested the battery under heavy loads (input power off and no other loads running) I ran the system with a blow dryer and space heater both going on full for a minute. Resting voltage before was 24.4v, but after loads applied it went to 23.25V and held steady. When loads turned off, it went back to ~24.4V. Not sure how to read that - what does it tell me about the life left in the battery?


  • PhotowhitPhotowhit Posts: 4,764Solar Expert ✭✭✭✭
    is this a standard flooded lead acid type forklift battery?

    Did you check the specific gravity, after the hard winter, and do corrective equalizing? Do you do monthly equalizing (or 2x a month equalizing if manufacturer suggests it)? Forklift batteries require a regular maintenance equalizing, and if chronically under charged over a period, likely need corrective equalizing.

    I've found my forklift battery to be amazingly resilient. You should know better than anyone the state of your battery. The heavy likely 2500+ watt load should drop the battery voltage. That's a bit more than I would suspect, but recovering after is a good sign.

    BTW- If you have a GB battery, they over rate the capacity of their batteries in the 20 hour rate. Their 12-85-13 which is 510 amp hour at a 6 hour rate is more like 660 amp hour in a 20 hour rate.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do
  • mcgivormcgivor Posts: 2,391Solar Expert ✭✭✭✭✭
    edited April 2 #3
    If I were in the predicament explained my first course of action would be to eliminate all loads and charge the hell out of the battery, with everything available, then equalization after equalization at ~32v  until the SG is where it's supposed to be, sounds like capacity is lost due to chronic undercharging. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • EstragonEstragon Posts: 3,006Registered Users ✭✭✭✭✭
    FWIW - I've had a similar problem, though with L16s not forklift.

    The good news is if the battery was cool/cold and reasonably well charged before the panels got covered, and the only load was charge controller(s), sulfation will be slow to form and harden. If too far discharged, hard freezing is a risk. Mine got as far as sort of slushy electrolyte, but not a hard freeze, and recovered well.

    I'd second (third?) the EQ suggestion. As well as checking SG, you may want to use an IR thermometer to monitor battery temp in various spots. If the freeze was fairly hard, there's the possibility of expansion having created a cracked plate or internal connection, which might result in intermittent problems under load.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Posts: 28,137Super Moderators, Administrators admin
    Check electrical connections (and voltage drop) to the battery bank... It is possible loose/dirty connections to the cells, cell jumpers, etc. could be an issue too.

    With many fork lift batteries, you can check the voltage of each cell (under load, under charge, resting). Also, confirm the SG of each cell.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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