How to check main battery

Page may contain affiliate links. Please see terms for details.

Funkyboy

Active Member
Joined
Sep 13, 2016
Messages
353
Car
E class
Hi All,

Last few weeks been getting a few weird things happening when first starting car. Sounds like slightly struggling to start for micro second other things I've noticed screen went off them straight back on and this morning horn sounded when starting? It's a 14 plate E250 on 78k. I've had the car since it was 18 mths old so battery is original. Is there a way to test the battery to rule this in or out? Thanks
 
Book at battery and alternator test at your local Halfords (it's free), if the battery fails, get a replacement price from Halfords but also look online at Tayna in North Wales if you're happy to fit the battery yourself.
 
Hi All,

Last few weeks been getting a few weird things happening when first starting car. Sounds like slightly struggling to start for micro second other things I've noticed screen went off them straight back on and this morning horn sounded when starting? It's a 14 plate E250 on 78k. I've had the car since it was 18 mths old so battery is original. Is there a way to test the battery to rule this in or out? Thanks
It’s a10 year old battery giving up in the cold , I personally would just change it before it lets you down away from home on a winters night .
 
If you are getting below 12.3v at terminals (with engine off) your battery is in a low state of charge.

what you really want though is to stress test it, most motor factors/halfrauds/ECP etc can do this for you for free.

At 10yrs (if it’s the original) I suspect it’s on its very last legs, and any cold snap will see you stuck!

Tayna batteries online are excellent, Bosch S5 or Yuasa next day delivery!
 
Here’s how to test a vehicle battery.
Check it is fully charged. This is best done with a hydrometer. If it’s a gel battery or you don’t have access to draw off the electrolyte then fully charge it.
Using a high rate discharge tester, put a load on the battery and check the voltage holds up. Different batteries have different capacities so the instructions or a general knowledge of what to expect would be useful. As a rule of thumb, with a 100 amp discharge, I would expect it to hold up to at least 10 volts for (say) fifteen seconds.
Any less than that indicates the battery may be faulty - your decision on whether to replace.
A falling voltage over that time indicates the battery is failing. This may be a dead or failing cell. A short circuit cell in a lead acid battery will usually ‘boil’ and give off a metallic smell - I think this is ozone.
There are testers that inject an ac waveform into the battery to test the internal impedance. These are good because they don’t reduce the state of charge, but tbh, I would only use one in conjunction with a high rate discharge tester - using both will give a clearer indication of the battery state of health.
Regarding losing settings etc when the battery is removed, my experience is that it depends on the vehicle. Some will be perfectly ok - e.g. my Jeep only lost trip data, A208 lost radio and window settings, and I recently replaced the one on the C-HR. This went well until I started the car and the reverse sensors and anti collision sensor fault lights remained on. These disappeared after two hundred yards.
 
Personally I would not write off your battery just yet. Instead I would invest in a good quality battery charger/maintainer to give it a new lease of life.

Something like a CTEK MXS 5.0 would be ideal, priced between £50 and £80 depending upon where and when you buy it. NOCO are good and well regarded too.

If you’d prefer not to spend so much them Lidl and Aldi often sell similar devices for between £10 and £20, and would almost certainly extend the life of your battery.

Sometimes batteries fail, however most people donnt charge or maintain their battery, and when it gives up they ask the vendor of car batteries to diagnose the problem.

Surprise surprise the answer is “it’s dead gov, you need a new battery” and you buy a battery from them. I’m sure most batteries are written off prematurely.

January is peak season for battery issues for a whole variety of reasons - with lots of associated posts on MBClub - but hardly anything for the rest of the year.
  • Cold temps reduce starting ability, reduced by up to 30% at 0 deg-C.
  • We use our cars less because dark nights mean we stay indoors more.
  • Most journeys have lights, wipers, AC, heater, heated seats, etc on.
  • Average journey length is short as we tend not to day trip, holiday, etc.
  • The car has been operating in the above conditions for 3-4 months.
Combined that lot is a perfect storm for a battery, and we replace it prematurely. In most cases the owner is the route cause rather than the battery being past it.

As John Lennon once said: All we are saying is give peace batteries a chance.
 
Personally I would not write off your battery just yet. Instead I would invest in a good quality battery charger/maintainer to give it a new lease of life.

Something like a CTEK MXS 5.0 would be ideal, priced between £50 and £80 depending upon where and when you buy it. NOCO are good and well regarded too.

If you’d prefer not to spend so much them Lidl and Aldi often sell similar devices for between £10 and £20, and would almost certainly extend the life of your battery.

Sometimes batteries fail, however most people donnt charge or maintain their battery, and when it gives up they ask the vendor of car batteries to diagnose the problem.

Surprise surprise the answer is “it’s dead gov, you need a new battery” and you buy a battery from them. I’m sure most batteries are written off prematurely.

January is peak season for battery issues for a whole variety of reasons - with lots of associated posts on MBClub - but hardly anything for the rest of the year.
  • Cold temps reduce starting ability, reduced by up to 30% at 0 deg-C.
  • We use our cars less because dark nights mean we stay indoors more.
  • Most journeys have lights, wipers, AC, heater, heated seats, etc on.
  • Average journey length is short as we tend not to day trip, holiday, etc.
  • The car has been operating in the above conditions for 3-4 months.
Combined that lot is a perfect storm for a battery, and we replace it prematurely. In most cases the owner is the route cause rather than the battery being past it.

As John Lennon once said: All we are saying is give peace batteries a chance.

Amen. You can just throw the old battery into the local river and give Mercedes or Halfords £100+ for a new one,

but if you haven't already been using either a battery charger or a battery conditioner, they can extend the life of a battery by many years
 

Users who are viewing this thread

Back
Top Bottom