Thread: calculating battery life/usage ?

if your in the middle of nowhere by yourself and you flatten your battery your stuffed

i think i'm right Amps = watts divided by Volts, you need to work out how many amps you are drawing first.

16amps is a pretty big draw, i wouldnot be chancing my start battery

a few options i can think off

1. install an aux battery, if your rangie already has the second battery cradle than you just need a battery (deep cycle) and a bit of cabling

2. install a low voltage cutout, similar to the one they use for fridges, cannot remember what voltage they cut out at but it should leave enough power to start your rig, not sure it would work to good at 16amp draw

3. carry one of those portable jump start kits just incase you drain the battery

a deep cycle battery is a little easier to work out, just divide the capacity of the battery (say 80amp/h) buy yoiur current draw (16amp) which will give you 5hrs, i don't have a clue how a start battery preform under a constant current draw.

keep in mind that your alternatorwill never fully charge a battery, so i'm told anyway

if its 2hr max without the car running you may get away with it

is this a once off use of the equipment?

i'm sure there will be somebody with a bit info than i can supply

thanks for the 80amp/hr info.

It won't be a one off but I don't use the RR as a daily driver. I go off road maybe a couple of times a month. I was hoping to get away with using only one battery but would rather buy a second than drain the starter battery.

The use is usually all day with about an hour or so stopping to refuel, (me, as in lunch). The 200w device would not be running if the vehicle was not running, well not for too long anyway

Hi Stevan, as long as you DO NOT use your gear after you turn the engine off, you shouldn’t have any problems.

For on road use, while the engine is running, everything is being powered by the alternator, so the state of charge of your battery is really irrelevant and if you are going to be putting in those sort of hours driving, your battery is going to be fully charged even while operating all your accessories.

A totally different situation for off road use.

While 4x4ing there is the potential of flattening your battery while driving because the engine may not be turning fast enough to allow the alternator to supply all the current needed to power your accessories and in this situation, you will be drawing current from your battery and and if you drive long enough at low speeds there is a real chance that you will flatten your battery even with the engine running and unless you let your engine idle with everything turned off, after you have done some slow speed off roading, you could very well find yourself having a low battery that will not start your vehicle again.

There is a lot more to it but this is the basics.

Cheers

Originally Posted by weeds

keep in mind that your alternatorwill never fully charge a battery, so i'm told anyway

Hi weeds, in normal on road use, this is an urban myth.

If the vehicle is doing more than 15 minutes driving each time the motor is started then there should be no problem getting any automotive battery(s) up to at least 85% charged, just running around town but once you take the 4by for a long trip, as long as your electrical system is functioning properly, there is no reason why you can’t get your battery(s) up to at least 95% fully charged.

As to whether you can get them to 100% charged is a bit hard to check for ( no matter how you charge them ) as there is no effective way to measure the exact state of charge while the battery is in the vehicle.

Cheers.

Originally Posted by drivesafe

Hi Stevan, as long as you DO NOT use your gear after you turn the engine off, you shouldn’t have any problems.
Cheers

As I only use the RR for off road stuff it looks like I'll have to factor in getting a second battery , bugger!