This is an old thread, however somebody may have a similar issue in the future. The battery in the forklift is old. Automatic chargers are GREAT with new batteries. However with old batteries, the batteries develop a surface charge, and the charger shuts off. The smaller charger worked better because it charged the battery slower and much longer, and did not shut off. A smaller charger is only harmful to a battery "if" it does not fully charge the battery, and if the battery does not get to the gassing stage to mix the electrolyte... Other than that, it is always better to charge slower than faster, however in conventional warehouse environments, it is often necessary to get machines back in service quickly. I am dealing with a similar situation with a machine with a battery I bought that was completely dead ( 9 volts out of 39). The proper charger would only run 20 minutes. I now have a small 50 amp charger on it, been running all day. The battery "is" gassing, so I l know that it is getting a good charge. This is a 800 amp hour battery.

No, I don't think it is right that "should battery boil every charge". The correct way is that battery should not boil. In anytime when you charge. When travelling around the city, I would like to charge laptop and camera with power inverter. The tool that friend recommends to me is Bestek 300w power inverter. No battery boil when charging. So if you want to get more information about this too, you can search bestekmall on Google. Have a nice day.

The stamp is under one of the plastic covers that cover the intercell connectors (the lead bars between the cells). It is almost always on one of the ones closest to the positive battery cable.

There should be a 3 part number. for a 36 volt 18-100-17 is an example. (some manufacturers add a letter or two in there. EX: 18-100D-17)

18 cells (36V)
100 amphours per positive plate.
17 total number of plates per cell.

(17-1)/2=8 positive plates
8x100=800 amp hour battery.

One thing you can be assured of this battery will not get better over time & you will be running undervoltage on your eletrical/eletronic components which will cost you something as they require replacement (motor brushes/commutators, contactor tips, switches, controllers, etc).

Thank you for the replies! Johnr I looked and could not see a stamped part no. on battery. I was not able to measure voltage after Fri charge as I had to leave before they could cool down; this morning after sitting all weekend they are back to same 2.03v on all but the two weaker ones, which are again back at 1.97v each. I tried my 6v 15a car charger across these 2 cells but they pulled to much current and shut my charger down after a couple seconds; put a 3rd in series and the charge was 15 amps for about a minute, then dropped to 1-2amps, telling me the weak ones have enough internal resistance to come up in voltage limiting current. Gauge does say 10/10 full charge on forklift. Seems we will not get >2.1v min I read about for cells to not sulphate... Since we only need about 15 minutes at a time a few times a week, this battery works enough for us but from all your comments it appears it would not work for someone who needed it 6 hours a day.

FYI - after full charge and appropriate cool down - each individual cell, when in top condition should read 2.2 volts when full charged and the total voltage reading for the 18 cell battery should be 39.6 volts. Based on the readings you provided your battery may have serious issues. Measuring cell volt shortly after taking teh battery off charging will give you a false reading - the battery must cool down to allow the electrolyte come up to the proper specific gravity.
Secondly, you cannot not go by the case size to determine the capacity of the battery - various ahc batteries use the same physical size case. The battery type (eg 18-85-21) may be stamped in the case or on an applied lable to the or stamped on one of the lead intercell connectors around the positive terminal.

One other reason for electrolyte "boil over" is overfilling the individual cells. The cells should only be filled to about 1/2" below the bottom of the filling hole to allow space for electrolyte expansion from gassing during charging.

Finally, when an equalizing charge cycle is selected the total charge time of a discharged battery (80% discharged) is ~16 hours or twice as long a normal charge cycle which is ~ 8 hours. Equalize charges are some time termed over the weekend charging vs over night charge cycle).

Thanks! I do not drive it so no clue how to make it go; I did not know it could be loaded into a hard stop like that. will test.

Oh, dah; I am thinking of my golf carts! had pix in mind of 2pc 6v in series, not 2pc 2v.... I have a couple chargers with 6v setting I have used on the old 8N tractor over the years.... IIRC, I have stuck em on batts with 4v output with shorted cell and I had control with like 8 amps or so.... I will try that. Thanks for correcting my mind-pix! As for the rest of the cells bothering the 6v charger, they won't if I just leave batt pack unplugged from forklift - they are just open circuit then and not in the picture.

A quick way to test the 2 weak cells is put a volt meter on each one and put the battery under a high load by pulling the tilt lever back and letting mast come back and stop while still holding the lever on. Hold the lever there and watch what happens to the voltage. If it drops and continues to drop below 1.7 volts the cells have a major problem. A 12 volt auto charger is going to freak out if you connect it to only 2 cells. The output amperage will go way up and trip the circuit breaker in the charger. It probably would even do that connecting to 4 cells.

Thanks to everyone for the wonderful feedback!!!!

When I said 20 amp rate, I meant that is what we charged at. As electrical engineers, we have all kinds of meters and things and 20-25a was the charge rate we used to have; I don't think we ever left it on long enough to see that drop below about 18 amps (we would not leave it on overnight when no one was here). When I said we did this for years, I meant on previous smaller (prob about 400ah) forklift. Sorry for confusing info!

Our battery is 18-85-21, verified by physical size, so rated 850ah.

We used our old 25 amp charger for 1 yr after getting this Yale Type E model ERP035TFN36SE082. Nameplate states max HA 1100 (6 hr rate) so that seems to jive with the 850ah real rating.

New to us (used) GNB model FER100 18-750-S1 automatic charger/equalizer on 240v 1ph input is outputing 200a at start dropping to 150a in a minute or so, then 100a around 5 min on, and now around 75amp 15 min into a charge.

Was last charged a few days ago - thru full cycle to auto shut off. Directly after which voltmeter read 3 bars (yellow) up (out of 10 total). That is when we smelled the sulphur smell.


We have often seen the voltmeter at near full scale. We unload a couple skids every other day off 18 wheeler trucks.

We can smell sulphur smell now, 15 minutes into the above charge cycle and the occassional bubbling.

Volts before this charge: 1/2 of cells @ 2.03v, most rest 2.01 thru 2.04, with TWO cells at 1.97v.

Overall batt reads 36.41v, yet only registering 3 lites up on voltmeter. If this voltmeter is like most others, then range is 31.14-36.98v; hence our 36.41 SHOULD be reading 9 out of 10 bars! So maybe we don't have a battery issue but a flaky voltmeter issue?

I recall similar experiments even with the old smaller charger and seeing voltmeter not seem to match the actual 36+v battery...

15 min into charge I checked voltages while charging: mostly 2.5v with the two low ones @ 2.2v -- this seems to tell me those cells are good (not high impedance) and just need equalizing up to match the others.

45min into charge and it is still 79a. most cells now 2.55-2.67, the weak 2 2.45-ish....

I don't like the equalize function because it seems to me in order to bring these two weak cells up it will overcharge all the others.... seems like I should just bring a car charger from home and put it on the 2 week cells (luckily right next to each other) and equalize them myself without beating the others.... What do you think of this idea?

I appreciate all your great comments! Thank you.

what edward hit on sounds about right....

you never noticed the boiling with the smaller charger because it was not charging the battery at the amp rating it should have been.
Those big batteries when discharged can charge as high as 150A when the charger is first turned on and yes... the cells will boil somewhat. As the charge increases and the cells become charged the amp rate should drop back and the finish amp rate should be considerably less, probably around 50A.
You will see bubbles rising out of the plates and sometimes you might even smell the hydrogen gas.
Now if it is vigorously boiling and stinking badly of rotten eggs you have a problem (along the lines of what edward said)
If you notice any smoke coming from any cells while charging stop charging it and get it repaired asap, the cell smoking is shorted.

You can get a general idea about how the condition of the cells are by taking a volt reading on each cell before and after charging , they should top out around 2.25v per cell (on a good battery). If you get much of a variance (1v or more difference) between cells there is a problem and the bad cells should be replaced.
Or if the battery has not been equalized in a long time sometimes that can fix the uneven cells and bring them all back up within expected ranges.
Get a hydrometer also and check the specific gravity on each cell, the acid level can play a part in how the cells charge also... if the acid content is low then the cell will not charge up, therefore you will get a shorter run cycle between charges. Only check the SG after charging, not before. If you do have a low SG after charging call your battery company for assistance. Adding new acid can help but let them do it if it can be done. If the battery is old then adding acid won't help much , chances are the cells are just sulfated or at the end of their life.

batteries will (and should) produce gas (boil) both while charging and while discharging. this is correct, you most likely have ruined your battery (big money down the drain, penny wise but pound foolish) by undercharging for far too long, and now the charger is 'trying' to correctly charge your battery.
I am assuming your truck must be a very small truck, and your use of "AMP" is ambiguous. tell us what the truck model and serial number is, and what is the AMP_HOUR rating of the battery, the charger and the truck, and we can give you more exact information.

What is capasity of the battery???Do you charge tham with standard charger or hf???
If someone sold you charger he MUST to know all details for correct equipment.
Acid battery goes in gas phase( cell charged over 2.40volt) and in that phase you will get boil but it is important that current is correct.When I say this I think that you dont charge battery of 240Ah with charger of 100A it will burn her.If you use 100A charger battery Must be 620Ah.It is 6/1 for acid standard( Wa) or 5/ 1 hf( W0Wa) that write in manufacturer books for chargers.
From this you can look your battery and charger and know what you need.