In one of those moments where the Internet actually did something useful, Batteroo's $2.50 sleeve to improve the life of batteries received a sound pasting.

Bob Roohparvar, owner of Batteroo which is developing the Batteriser claimed that typical alkaline batteries use about 20 per cent of its available energy. The reason for this high inefficiency is that electronic devices are finicky; they need a steady voltage of 1.5. When an alkaline battery drops below 80% capacity the voltage also drops to 1.4 or 1.3. At that point the device will read the battery as dead, leaving 80% of its juice unused.

The Batteriser, Roohparvar claims, is a miniaturised device that boosts the voltage back up to 1.5, and maintains it there until every last drop of energy is extracted from the battery.

It sounds reasonable and at least does not require you to believe that the laws of thermodynamics have been thwarted. It is a boost converter circuit shrunken down to fit into a sleeve that slips around the battery. It boosts whatever battery voltage you have up to a constant 1.5V. So it could work. Theness and the EEV blog tested out the claims and came up with pretty much the same results.

Theness knocked the 800 per cent figure out of the water because the maths did not add up, but 500 per cent would still be pretty cool, but it looks like that does not stack up either.

Then there is the problem that the voltage of an alkaline battery drops as capacity drops, the big drop off doesn't occur until around 82% of the capacity has been drained, and therefore only about 18 per cent remains.

All of this means that the Batteriser, if it works optimally and does squeeze every last drop out of alkaline batteries (and does so safely) is probably going to increase typical battery life by about 20 per cent, not 800 percent.