Team-BHP - Replacing battery with one of a lower AH (amp-hour) rating?

My Grand i10 1.2 Petrol AT battery is due for replacement. I checked the OEM battery which is 40 ah. But none of the dealers are having 40 AH batteries, including online portals like batterywale etc. They all have 35 AH batteries only.

My question is, is it safe to go ahead with a 35 AH battery? Will I encounter any problems?

Ah will just give you an estimate of how long a battery will last at that current level. eg. the 35Ah battery will supply 35A for 1 hr before the battery drains out while the 40Ah will supply 40A for 1 hr. This doesn't mean the batteries can't supply higher current, it's just that they will last for a lesser time on a full charge.

If you don't have any electrical accessories that would require the higher juice battery (eg aftermarket music system), it should not pose a problem keeping all other parameters of the batteries same.

You will also have to consider not using music system (or reducing the time) with the engine off.

The battery is mainly used for starting the car and supply power in case the power demand exceeds the alternator capacity. The battery also acts as a surge protector absorbing any power surges by the alternator. So if you have a bone stock car with no 100/90 headlamps or Aftermarket amplifier and stereo, you can go for the lower ampere battery without issues.

For example, if the alternator is rated @ 120Ah, from the moment the car is started, all the power needs in the car is provided by the alternator including charging the battery. Now if the sum of the electrical load exceeds 120Ah then the excess demand is provided by the battery. In such a case, the battery is in drain-in-progress condition.

However, if you are someone who uses the stereo with the car turned off, in such case the amount of time you can use the stereo before the battery charge reaches below the minimum threshold to start the car will be less. Say, with 40Ah battery, you could use the stereo with the engine turned off for 1Hr before the battery charge reached the minimum threshold. In the case of 35Ah, you can use the stereo for 45 mins by the time the battery reaches the minimum charge threshold.

Note: The minutes/hours are just indicatory for the example.

Quote:

Originally Posted by sagarpadaki (Post 4504062)

Thanks, I forgot to mention in my original post i am running a Dashcam and TPMS (Tire pressure monitoring system). Both are connected to the two 12V sockets in my car. Hope that isn't an issue with the lower Ah battery.