How do you test your sealed lead acid battery?

[ving (David)]

got a problem with multimeters? I use one.... or my tongue

[rogerg (Roger)]

I have one of those kind of things from K-Mart, it has a 17 amp hr battery in it. Problem is, the battery will die before the cheap indicator tells me it's empty. In fact, even when it's dead and unable to power the laptop the indicator stays on green.

Hence I have given up on it.

Roger.

Originally Posted by h0ughy

I have one of those with a 110AH deep cycle sealded LA battery. excellent, easy to see whan you need a charge.

[rogerg (Roger)]

Originally Posted by ving

got a problem with multimeters? I use one.... or my tongue

I just thought there might be a neater solution - single digital readout with no buttons or anything to get in the way. Thing with the multi-meter is getting it out, putting the pins on the terminals, turning it back to the right setting after using it for something else, and then turning it on. I thought maybe there'd be a nice solution I could just wire in to my plugs, wave there the whole time dimly illuminated or the like.. which, sure, I could do with the multi-metre too.... but..

Roger.

[ving (David)]

Originally Posted by rogerg

I just thought there might be a neater solution - single digital readout with no buttons or anything to get in the way. Thing with the multi-meter is getting it out, putting the pins on the terminals, turning it back to the right setting after using it for something else, and then turning it on. I thought maybe there'd be a nice solution I could just wire in to my plugs, wave there the whole time dimly illuminated or the like.. which, sure, I could do with the multi-metre too.... but..

Roger.

I know roger, it such hard work

how about some sort of built battery level monitor between the battery and device?
sorry, i am not much help am i?

[RAJAH235]

Roger, my small veroboard unit is just 38 x 38 mm sq. & is screwed to my base as shown. It is wired directly across the battery/socket assy. Nothing to connect. It automatically gives an instant visual indication if the voltage falls below your set value. Very simple to make & also in operation.
HTH. L.
ps. It is waterproofed, naturally.

[cjmarsh81]

Rogerg, is the battery level meter real or a sticker? lol. If it came from K-Mart I would not be surprised. By the way, those 17Ah from Kmart are more like 10Ah. They use cheap batteries. I was looking at one myself and ended up going to battery world and getting a Projecta 17Ah. You can tell the better batteries by the weight.

[GrampianStars (Rob)]

G'day Y'all
In the field I use the 17Ah jump start from supercheap [the yellow one]
they've now got a 24Ah kit with multiple outlets on

[Karls48 (Karl)]

Little light on lead acid batteries

Any battery testing (to give meaningful result) must be done with a load. Measuring voltage with voltmeter without the load tells you nothing. Common 13.8-volt 7A is rated at 20 hours discharge cycle. That means it will supply 0.35A of current for 20 hours before it is discharged. Increasing the current drawn from battery over the rated discharge current will decrease effective battery capacity. Drawing current smaller then rated discharge current of the battery will increase effective battery capacity. To put it in other words, if you have 7AH battery and you draw 1A from it, it will be able to supply 1A of current for about 5 hours (5 AH). But if, using same battery, you draw only 0.1A of current it will supply that current for about 85 hours (8.5 Ah). For exact numbers you have to look up manufacturer Discharge charts, as it will vary from one brand to the other.
To test 13.8V 7AH battery:
Fully charge battery
Connect 47R 5W wire wound resistor across the terminals
Battery Ampere Hours / Discharge rating (7/20=0.35)<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o:p></o:p>
Resistance needed to get 0.35A at 13.8V – Voltage * current (13.8*0.35=48.3). Nearest value available is 47R.
Now measure voltage across the battery terminals:
13V – good
12V and above - OK
11V – and above no much left
11V and below – stuffed.
You may rejuvenate (sometimes) stuffed battery by discharging it to 10.5V and then recharging it slowly. Repeat process 5 to 6 times.
Regards
Karls48

[Vermin (Tom)]

I've never had any luck trying to rejuvenate SLAs, which is why I have a battery voltage monitor with audible low alarm - to prevent the battery discharging below 11V.