The Tech Blog

I was looking for a long-term rechargeable option for a few household gadgets. I knew 1.5 V lithium AA cells existed, but I had never used them till now. So I thought today was a good day to explain how they work.

Lithium batteries in consideration are of two kinds. The first is primary lithium AA, using lithium–iron disulfide, or Li/FeS₂. It is non-rechargeable and naturally delivers an alkaline-compatible 1.5V. These cells are light, handle high loads and cold weather well, rarely leak, and branded versions can have a shelf life of around 25 years. They are roughly ₹200-₹300 per cell in India, they suit outdoor sensors and “put-and-forget” devices.

The second kind fits a rechargeable lithium system inside an AA shell. It usually contains a 3.7V lithium-ion cell, a protection circuit, and a buck converter that steps the output down to a steady 1.5V. USB-C versions also contain their own charging circuit. The 5V input charges the internal cell, while the buck converter powers the gadget. So every battery is has a tiny charger, protection system, and regulated power supply.

They can do approx 1,000-1,200 recharge cycles. Real life as always depends on temperature, discharge depth, charging quality, and how long the cell stays fully charged. Four-cell packs in India cost around ₹1,200-₹2,000. A good thing about them is they always provide a steady 1.5V compared to alkaline ones that start at 1.5V and drop to around 1V when dead. Lithium versions are also lighter and often provide more usable energy.

There are trade-offs. The converter adds standby drain, switching noise, and a current limit. That makes these cells less suitable for wall clocks, low-power remotes, and sensitive audio equipment. In the end, the choice depends on the device and how you use it, rather than one chemistry being universally better. Please know that Lithium ones are a valid option for your future needs if you want to spend more.

There has been a lot of hue and cry around AI data centers. I think a good part of it is valid, because big ones can stress the local power grid and water systems. The energy side is harder to solve as every calculation needs electricity. The water side is more interesting, because water is often used to move heat. Let’s discuss the latest tech trying to reduce that.

From the basics, almost every watt entering a server becomes heat. A 100kW AI rack is close to a 100kW heater. If you remove heat using air, you need airflow, fans, cold aisles and chilled water. Traditional cooling often uses an open or semi-open evaporative path. Water takes heat from the chiller loop and some of it is intentionally evaporated in a cooling tower. This works because evaporation carries a lot of heat. Water demand can peak on hot days when cities and farms also need water.

In a closed-loop system, a water-glycol coolant flows through cold plates on the chips, picks up heat, goes to a coolant distribution unit, then to a dry cooler that works like a radiator. The same coolant keeps circulating. NVIDIA’s reference talks about 45°C coolant going in and roughly 55°C coming out. That higher temperature loop matters because warmer coolant creates a larger temperature difference with ambient air, improving heat transfer in dry coolers and reducing the need for water-intensive cooling towers.

Microsoft, Google and Meta have been pushing liquid cooling and higher temperature operation for the same reason. Recent lifecycle work suggests advanced cooling can cut total water use by roughly 31-52% versus traditional air cooling. An NVIDIA white paper says cooling-tower-based systems can use about 10 Million litres per MW-year, while warm liquid loops with dry coolers can bring that close to zero in good climates. So good from the local nature PoV.

I think this should be considered by every new data center being planned now. A site already built around air cooling or evaporative towers may carry that architecture for years, but new builds still have the chance to choose a lower-water heat path from day one. I hope India follows the newer tech.