How to meter mah in a battery

[laganm21]

I have a Home made Hump pack that a buddy of mine made a while back and i don't know the mah on it, how do i meter this with a multi meter, i was told once to put the batter under a load and mesure it in series get the current draw and use the trusty Ohm's law but i am confussed so any help will be nice

 

[Sprint 77]

cycle it up then drop it down and charge it back up how much your charger puts in after the cycle will be a what its useable to your car mah you would like to hve a min of 1500 mah with our big gas tanks and high drain servos. 3000 and bigger are what most of us run.

 

[laganm21]

I have a Old school battery charger, just a turn dial 15min quick charger its rated at 7.4v at 1500mah 20min of charge time, thats the problem i am having, with the stock 6v 1500mah battery that came with the Ramp MT it will last me a tank, witch is fine by me because i know when it need to be charged, but this new battery that i don't know the mah on i don't want to over charge it because my cheap quick charger don't have a peak charge cut off

 

[hamster huey]

Charge it until it gets pretty warm but not hot. Use a bulb discharger. The bulbs are 5amps a bulb. I would use a 20 amp (4 bulb) or 10 amp (2 bulb) discharger. Put the fully charged pack on it. Time how long it takes the bulbs to dim. Do the math. Say it dies in 6 minutes pulling 20amps, that would be 2,000mah. (2000mah is 2 amps for one hour so 20 amps is ten times the draw and ten times less runtime so it would be 6). This is a rough estimate but it will give you an idea. Servo leads are rated for 5 amps before melting so they don't pull very many amps. My 1500 battery lasted 3 tanks but got weak on the second. I would say if you can only make it less than 3 tanks its less than 1500 or not taking a charge.

 

[hamster huey]

Oh thats 5 amps on 6cells so 5cells should give maybe a minute or two less runtime. Someone correct me if Im wrong its been a while. I would also recommend the duratrax digital pirahna on ebay usually less than $35 shipped. Its a good beater charger. The digital display will tell you MAH going into the battery, but it does not discharge though. Still useful. Also if you know the charge rate of your dial charger you can put a dead battery on it and time how long it takes to get pretty warm and then do the math.