[lynnandrob]

Hi,

How do I find out how much power is in a 12v/80ah battery.
At the moment I have a 12v/80ah battery connected to a security camera system but would like to measure the power as it dissapates.
I have a standard multimeter which can handle 10amps max so I know I can not just bridge the terminals.
ive read that you shouldnt let the battery drop below 50% before charging it,and so need to find out how long the system can run before i need to recharge.

Thanx.

[lachlanandmarcus]

Some electric fence energisers have built in meters, might be able to borrow one? Mine is a speed rite one from rappa. Doesn't show exact amount left but does show proportion left in series of green/ red lights

[fl206]

From http://en.wikipedia.org/wiki/Lead_acid_battery#Voltages_for_common_usages

If it's a lead-acid battery, fully charged would be measured as 12.6V with only your multimeter attached to the battery. Bridging the battery with your multimeter is fine if you're measuring voltage as opposed to current.

50% discharge should be around 12V.

[bazzais]

Use a hydrometer if its lead acid.

If its a dry cell - run it till it runs out then the next time take it to charge it a day earlier than that

[bazzais]

Security camera should last for ages unless it has lights, IR, wireless or on a huge 100m bnc cable up to the sheds.

[mab]

yep, hydrometer is by far the best way to measure state of charge, unless it's a sealed battery.

you can measure current drawn by the load and multiply by time the load has been on.

if in doubt; recharge.

[lynnandrob]

using a digital battery analizer ( sealey BT2002 )
i can see the health of the battery and the charge from 100% to 0% which are  shown in bars and percentages,you can also whatch the volts as they drop on the screen