Laser Rangefinder wiil not recharge

It doesn't sound like a fault specific to a rangefinder, more like a common problem with battery powered equipment left to go flat and kill the battery ... does the case open easily?

Rechargeable battery failure because it has been left in a discharged state? Maybe it's either been put into storage with the battery low and/or battery self discharging?

The case will have been put together in one of three methods

1. Glued together. This can be problematical to get apart.

1. Clipped together. The two half can be prized apart by inserting a thin metal implement in the crack. A thin butter knife can work as can a metal spudger.

2. Screwed together. You will often find the screws under the rubber feet plus one or two either in the battery compartment or under the sticky label that has the model number.

The battery may have a small connector or may be soldered in. With luck it will have a model type and a replacement can be obtained from the usual sources

"Sndway H-D510A Laser Distance Meter Mini Rangefinder 50m Laser Range Battery. 3.7V 850mAh lithium"

It's a single cell device, which cannot be reverse-bias-damaged by discharge.

My experience is though, that lithium really doesn't like to be flattened all that much. My camera is like that, a 3.7V single cell pack, and it has flattened on at least one occasion, by it not entering its sleep state properly. it was drained the next time I went to use it.

What I do for the camera, is when the camera has been put in an unsafe state, I pull the battery for 15 seconds, then shove it back in and then the camera "sleeps better".

The device in question, may not have such an arrangement (a separate pack which pops out). You can attempt to preserve electrically leaky devices, by leaving the pack out of them when not in use.

To maintain battery devices, it helps if the device has a fuel gauge, so you can ascertain how fast it self-discharges. On my laptop, I check it every three months, to make sure it isn't too low. It could actually go for longer than that, without maintenance, but as it ages, I keep an eye on it.

Devices without any sort of readout, are harder to judge.

The rangefinder Being a single-cell device, it should be harder to damage, but you never know. On my camera, the original battery died years ago, while the aftermarket replacement continues to function.

Paul

A lot of lithium cells can be superficially revived by charging them with a low current to bring the voltage up from zero. Set your PSU to say 4.1v and a current that's about 5% of the rated mAh (ie 850mAh*0.05 = 42.5mA, call it 40mA in round numbers). Apply to the battery terminals and measure the cell voltage as it gradually rises. It will rise quickly to begin with then hopefully slow down as it takes charge - if it gets up to 4.1v quickly then the cell is toast, but if it sits around 3.2-3.4v for a long time then it's charging happily. I'd probably apply a full 'gentle' charge cycle like this to confirm charging behaviour is as expected, which should take some hours (20h if you follow the 5% rule).

Once charged you can put it back in the equipment and it should work, but watch for unexpected shutdowns or reboots which are caused by high current pulses meeting a too-high internal resistance, another sign of an aged battery. It should also now charge as normal, now the cell voltage is in the normal range.

You may find the runtime is reduced as the capacity has reduced due to the damage, but the device may still be usable with a shorter runtime.

In the case the cell needs replacing, if it only has two wires you can probably replace with another lithium ion cell even of a different physical size (eg an 18650 cylindrical cell). If more than two wires then the rest are either comms or a temperature sensor and you likely need to replace like with like.

Theo