DIY Lithium-Ion Solution for AA Battery Replacement

AA batteries can leak fluid, whether they are alkaline or carbon-based. This can cause significant damage to the device's circuit board and battery contacts, especially alkaline batteries. If you are experiencing this problem and happen to have a bunch of lithium-ion or 18650 batteries on hand, you can consider making a DIY solution.

There are three basic types of solutions: LDO linear voltage reduction, buck voltage reduction circuits, and charge pumps.

1. LDO is not ideal for battery-powered devices because it is too inefficient, wasting over 60% of the electrical energy and causing shorter battery life compared to alkaline batteries.

2. Charge pumps are a good solution with high efficiency. If you cannot find a suitable chip, TI's TPS series has one with a static current of 30uA, which may be slightly high, but the efficiency is over 95%.

3. Buck circuits are generally not favored by most people because they have relatively high static current. However, the TPS62201 solution has a static current of 15uA and a theoretical efficiency of around 85-90%.

TPS 6220x series specifications:

First, a simple circuit was constructed with only three external components: input and output filter capacitors of 10uf (preferably surface-mounted with low ESR) and an output inductor of 10uh.

After several days of testing, the quartz clock operated normally with no abnormalities in accuracy.

Under normal load conditions of 0.51ma, the efficiency was around 85%, which is consistent with the data sheet. Using a discharge platform of 3.7V lithium-ion battery and 1.2V AA battery, a 1500mAh lithium battery is equivalent to about a 3800mAh AA battery. Considering the duty cycle of the quartz clock current is about 0.2-0.3, it is estimated that it can be used for 2-3 years, and the actual effect can be observed after DIY.