Battery Life Question

[Calavera]

I don't get a chance to drive my car as often as I'd like; I notice that if I leave the car for 3-4 weeks the battery seems to run flat and I need to take it out of the car for a charge. I have an alarm / immobiliser fitted but I don't think it is too heavy on power.

Do others experience this ? How long would you expect the battery to last on a full charge if the car is not on the road.


Cheers
Richard

[Chris Williams]

I think a 'lot' of us experience a battery that discharges when not in use. That's why you see a lot of DeLoreans with battery master switches installed. I'm sure someone can supply a reason as to where the juice goes!
Chris

[Dan6457]

Mine does that. I put it down to battery getting on a bit and maybe the alarm, central locking, radio, sub woofer all in standby using a little bit. I just top mine up from time to time with a charger connected on the jump start terminal. I don't isolate my battery because I'd have to re-set my radio settings and alarm system, and clock each time!

[NickT]

The largest battery drain on the car of 13mA goes to the central locking module. (This is assuming no extra wiring like alarms, ICE etc is installed!)

A different pair of transistors and relays and it will drop down to 1.3mA !

It also depends on the type of battery fitted.

You can remove a battery lead and put a current (amp) meter in series between the removed lead and battery terminal and note what your battery drain is.
Ideally this should be less than 50mA (0.05 Amp)
If it is more than this then remove the fuses one by one until you find which circuit the battery drain is on.

4 weeks = 28 days = 672 hours
0.05 Amp drain for 672 hours is approx 33.6 Ah (Amp Hour)

If you can reduce the standby to 20mA (0.02 Amp)
0.02 Amp drain for 672 hours is approx 13.44 Ah

I think the oem battery is rated at 60 Ah
I wouldn't put anything less than 75 Amp Hour.

I haven't installed my battery isolator yet, to give an idea I left my car standing for 8 weeks, the battery was 12.3 volts and it started straight away.
I did have to drive it for 5 miles before the gearbox solenoids operated smoothly again !

Definately a good idea to have the isolator switch though

NickT

[bozzzydmc]

Good answer as ever MrT

Just bought one of these handy little thingies...

http://www.maplin.co.uk/Search.aspx?cri ... ce=15&SD=N

[Calavera]

Thanks guys and cheers Nick that’s pretty comprehensive answer. I suspected that it was a common issue I'm just curious if 4 weeks is a good average or a bad one. Mike that's cool looking gadget , I might pick one of those up.

[NickT]

bozzzydmc Wrote:Good answer as ever MrT

Just bought one of these handy little thingies...

http://www.maplin.co.uk/Search.aspx?cri ... ce=15&SD=N

No probs Calavera, hope it was useful :wink:

That looks like a nice nifty gadget Mike.
It would be useful to see how much current each circuit actually uses on the car.

NickT

[TheOriginalMrP]

I think ChrisS is making some locking modules with this lesser current drain. I've left my car 6 weeks (With Chris's prototype module fitted), and it's started on the button fine, even with my previous knackered battery on it. I only changed the battery as an hour of ICE use would make it drop to a level where the car would be lazy starting.

Ben

[Tourettes Tony]

i always diconect mine, but am thinking of buying one of those remote battery switches in practical classics around £60

[Darren C]

Hi Guys,

I put a key operated battery isolation switch in the top right of the battery compartment. This breaks the Pos lead. A small hole is cut in the plastic cover about 30mm diameter for the key to go in. Simply lift the carpet and turn key. Having a key is better security than those flappy bright red rally type switches. Key, switch and spare key £20!

You can get them from HT Motor supplies on 01243 787471. Ask for Nigel or Duncan, mention me and they'll do you a deal. :wink:

Switches are all metal construction and high amp rated. Got them on all my cars now.

As for radio codes etc, you can put a single wire feed to bypass the isolator (fused at 5amp) straight to the radio permanent live. That saves re programming. 8)

And dont forget a pair of 8mm lugs from your local City electrical to crimp or solder onto your cut pos lead, so that you can fit them onto the switch. They'll either just give two away or charge 10p. Trust me it aint worth the paperwork for them.

Best Regards
D

[Rich Hanlon]

Has anyone tried one of those solar panel trickle chargers to keep things topped up? £15 in CPC...

Can either go via the fag lighter or can be wired in. I wondered whether to runa couple of semi-permanent wires from the battery, routed through to the rear deck.

Maybe wire up a jack connector or similar and sit the charger on there when the car's at home?

[Dan6457]

I plug my charger onto the jump start terminal in the back.

[NickT]

Rich Hanlon Wrote:Has anyone tried one of those solar panel trickle chargers to keep things topped up? £15 in CPC...

Can either go via the fag lighter or can be wired in. I wondered whether to runa couple of semi-permanent wires from the battery, routed through to the rear deck.

Maybe wire up a jack connector or similar and sit the charger on there when the car's at home?

I had that idea too Rich.
I bought one of these from "Maplins" for £10 at the time.
It would be OK to keep a battery charged up.

One of my (many) jobs was to do as you describe, in fixing the solar charger to the (north facing) garage window fixing wires around the garage to the car then using a multiplug to connect to the D.

I was thinking of putting a multiplug with wires going to the engine block (earth) and jump start post (permanent battery+). Fused obviously and no scotchlocks ! :lol:

One of my "to do" jobs when I get a chance.

NickT

[Darren C]

Hi,

Tried a solar charger £19.99 from Maplins. Made the battery "lazy"
Ended up having to buy a new battery.
Wouldn't recommend them. I'd go for a battery conditioner, works like a charger but only charges when the voltage drops, as required.

Best Regards
D