Main Aircraft Battery Wont Hold Charge R2 4 times

[TJSpectre130]

Model Aircraft HC-130N, No wires have been T/S yet due to Electrics only being called out to the last two problems, First time i was called out to the plane the battery was sitting at 15volts, this of course was during a -1 ops check and the battery was dropping rapidly with both inverters on, makes sense being that both were on without external applied. We charged the battery for 30 mins bringing it up to 25volts and doing the inverter check again ops check good. This took place on a thursday, this past tuesday we get called out to the plane to the battery only holding 8 volts, let me remind anyone that this is the 3rd one changed showing the same problems. I decide to change the battery again and trouble shoot from that point with a fresh battery, with that said our back shop is only day shift it took a few hours to get a new battery to put in. this was done on swings. With fresh battery in and one thing i wanted to check was to see if the Emer Exit lights all Extinguished once the button was depressed which they all did. Thats about as far as i got then shift change came. With all power off the plane there is no indication that the battery is powering any of the buss', you can here the Gyro winding down but i was told that its normal for it to take around 15 mins for it to do so. What my question is has anyone ever seen this happen before and where might be a good place to check first and so after. could the back shop bench charger not be doing a great job at charging them. Any help is appreciated

This is a 24v 36amp/h maint free battery with its own ground wire.

[n1dp]

Not familiar with the maint. free lead acid battery, but if you are on your second battery, I suspect the problem is in the aircraft. When you say everything is off, as you know, the battery bus is still powered. Looks like you have eliminated the emergency exit light extinguish? I'd ask if you can pull all the battery bus circuit breakers to see if some kind of phantom drain is there. Does your aircraft have two batteries in the compartment? Is there some kind of interconnect between the two?

[Nick-3g]

Is the DC Volts gauge set to BAT? The "Moving Coil" meter will drain the battery over night. Simple but sometimes forgotten.

[Ronc]

We have an airplane on our ramp here at Hurby doing something very similar as you described. I find this a little funny, is it possible that the AF bought a bad batch of batteries?

[tinyclark]

It would be easy enough to put an ammeter across the battery and see if there is any current flowing. Easiest way would be to pull the ground off and hook the ammeter up there.

[TJSpectre130]

thanks for the replies, this is how we solved the problem. We hooked up a multimeter to the open end of the battery connector, this allowed us to read the voltage and also view the drainage as it was happening. then with aircraft power off, we started to pull each batt buss powered c/b one at a time to see is the drain would stop. this lead us to the fire extingisher system. pulling that c/b stopped the drain from the battery. note the model aircraft has an INS batt which was uneffected from problem. T/S began with the Fire EXT system. knowing there is always power going to the discharge switch means that the Fire extingishing control valve assembly also has power going to it as well. This large relay assembly has several grounds built into it and is also case grounded, we ohmed every pin and per our diagram we found that every grounding switch in that relay was stuck causing the battery to drain. We r2 the assembly and no problems since.

tinyclark i had the same idea with the ammeter but ours was at pmel ?? for calibrations