Thread: Do I need to get a new battery?

Originally Posted by drivesafe

Hi dearot and if the charger is still in BULK mode this time, your battery is probably on it’s last legs and it is more than likely going to go flat by itself, in a sort period of time.

Hi John_W and 15 minutes is the absolute bear minimum drive time, “IF” the battery is in good nick and already fully charged.

In this case, dearot’s battery is not in a good state of charge, so 15 minute drives just worsen the problem.

I acknowledge your industry credibility but how does the maths hold up? 15 min with a modern alternator pushing 120a against probably no more than 300a but lets say 400a for 1 or 2 seconds to start the TD5. That is a ratio of about 135:1.
And my real world experience mostly doing about 7 min to and from work . My batteries never need extra charging and last the usual 4-5 years. How do you explain my observations?

Hi John and the battery is the ruling factor.

You can have a 1,000 amp alternator but if the battery is only going to draw 10 amps while recharging, time is need to charge the battery, not additional current.

If a battery is fully charged, it will use far less of it’s capacity to start a motor. A 15 minute drive is the minimum drive time.

If a battery is low, it will use much more capacity to start the same motor. You now need much more than the 15 minutes of drive time.

If a battery is fully charged but in poor condition, again, it will need to supply far more of it’s capacity to start the same motor

In Dearot’s case, he has a battery that is low and in a poor condition. He would need to drive for long periods of time, to allow the battery to get a moderate charge, or he can use a battery charger to supplement the short drive times.