Battery Charging - Advice

[santoshlv426]

I'm a slow driver and the car's ususally driven between 1500-2200 rpm. I am aware that the speed of the engine influences the current output of the alternator.
What about gearing down and "holding" the car in high gear ? Both with this or any car.
Would that provide current sufficient to charge the battery.
I'm one of the "once a week usage" with the car.

[scm]

I'm one of the "once a week usage" with the car.

Depends a lot on how long that once takes. If not long (at least an hour?) then you need to keep the revs up and/or use your CTEK.

[santoshlv426]

Well scm, it seems like what you suggest is what I need to look out for as I commute 60km max and around 30mins per journey.
I did change my battery early in 2024 and don't expect the same life from the Varta as I got from the original Jaguar battery

As an aside, the OEM batteries are definately manufactured to a higher spec than the aftermarket (Varta, Duracell) and is about doubt that of the aftermarket.
I learnt this when I made an enquiry for a battery for my Lexus from LExus themselves. They quoted me a battery 4x that of the aftermarket as it was a high capacity unit manufactured by Panasonic !

[honeybadger]

The alternator can charge the battery at low RPMs, but it does so very slowly. If you're running accessories like heated seats, screens, blowers, stereo, or headlights, the power from the alternator is first prioritised to keep these systems running. This means that only the leftover power, which could be minimal at low RPMs, is available to charge the battery. At idle, you might even be drawing power from the battery rather than charging it, slowly depleting it over time. Remeber, turning over a V8 requires a lot of power, and that needs to be put back!

However, this doesn’t mean you need to drive like a maniac to ensure the battery gets charged (though it’s more fun if you do!). As I’ve mentioned before, the output of an alternator isn’t linear — a modest increase in RPMs results in a significant jump in output current.

For example, an alternator output curve is shown below. It may not be identical to the one used in the F-Type, but it's similar in terms of rating and behaviour. Note that the speed is for the alternator, not the engine.

If we assume the car’s pulley ratio is approximately 2:1, this means that for every turn of the engine, the alternator spins twice. At an idle speed of around 850 RPM, the alternator would be turning at about 1700 RPM, which is less than a third of its rated power. However, as RPMs increase, the output from the alternator rises quickly. Full current may be reached by 2500 - 3000 RPM, but that's not an engine speed the car typically cruises at.

The point of all this is to know that on a drive your battery may not charge as quickly or as fully as you might think and that depending on your car's usage, a battery charger might be a good investment