Why does my car battery drain when turned off?
QUESTION
Hi John,
Always impressed with your informative videos.
I have a Ford Ranger PX 3.2 Automatic 2015 purchased new and 103k km on the clock so far.
During the first six years I had two batteries on it, the factory one for 3 years and 2 months and a century one for 2 years and 8 months.
After two recent incidents of the flat battery, I found about 2 amps drain current immediately after the car is turned off and stabilises at about 0.18 amps after approximately 15 min.
I had the car checked by the dealer they reckoned that the drain current reduced to 0.01A after 45 min but never happened with my own clamp amp meter.
I did seek a second opinion from an auto electrician who reckons it is normal to have 0.18A constant battery drain on modern cars while the Ford Australia's engineer stated maximum drain less than 0.05A in an Email conversation to me.
I checked another car, Volvo S60 2011 D5 with the same meter and the drain current gets to 0 in less than 5min.
Can you please kindly advise if it is an issue with the Ranger PX MK1?
Thanks for your help,
Ryan
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ANSWER
Ryan,
Getting 2-3 years out of a battery is completely normal. It depends how you use the car. Any instances where the car sits around for a while and progressively drains the battery will reduce battery life. Ditto, draining the battery in other scenarios - running appliances with the engine shut down, etc.
Cold cranking batteries (normal car batteries) hate being deeply cycled. It kills them quickly. It’s a function of their internal construction.
Cars impose electrical load on the battery when shut down. The CAN bus needs to be energised and the car needs to listen for the proximity key, etc. The initial higher current draw on shutdown is probably because other systems remain active - perimeter lighting, infotainment, power-off system self-check, etc.
0.18 amps is only 24W-h overnight for 12 hours, for example. An 85A-h battery (I don’t know the Ranger battery specs, but it’s probably about that) contains about 1000W-h of energy, so leaving a fully charged battery in the car for 12 hours consumes about 2.5 per cent of its energy, or five per cent for any 24-hour period.
If you leave the car shut down for a few days days, often, that’s probably bad for overall battery life. in that case, buy a trickle charger (about 1 amp) and plug it in. Or fit a solar panel-type trickle charger to the roof rack, and just set and forget (it’ll always trickle charge, whenever there’s ambient light.
Or just plug in a normal battery charger every Sunday, and recharge at 5-6 amps. Kinda like the same overall effort as praying to Jesus, only you’ll get a result.
Hope this helps.
JC
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