Power
Batteries and charging
The battery is usually the first part to fail, and almost every failure is caused by how the object is stored rather than how it is used.
Nearly everything rechargeable in this category uses a lithium ion or lithium polymer cell. Those cells are light, hold a useful amount of energy and tolerate hundreds of cycles. They also have habits: they dislike being stored empty, they dislike heat, and they lose capacity slowly whether used or not.
Reading a runtime
A stated runtime is almost always measured at the lowest continuous setting with no load. Real use involves higher settings and contact with tissue, which loads the motor and draws more current. A stated two hours commonly means forty minutes of ordinary use, and a dual motor design will halve that again. Charging times are stated more honestly, since they are easier to measure and harder to flatter.
Charging methods
- Magnetic contacts
- Two pins held by a magnet against the outside of a sealed shell. Nothing penetrates the body, so the object can be fully waterproof. Contacts can corrode if stored damp, and a proprietary cable is easy to lose.
- Open port
- A standard socket in the shell. Convenient and replaceable, but the shell has a hole in it, which limits water protection to splash resistance and invites corrosion.
- Induction
- No contacts at all, so the shell is fully sealed. Slower to charge and rarer in this category, mostly on premium designs.
Storage that preserves capacity
- Charge to somewhere around half before a long period of disuse.
- Store at room temperature, away from radiators and away from direct sun.
- Top up every few months rather than leaving a cell to drain completely.
- Dry the charging contacts fully before putting anything away.
A lithium cell left flat for a year often will not accept a charge again, because the protection circuit locks out a cell that has fallen below its safe voltage. That is the most common way a working device becomes scrap, and it happens in a drawer rather than in use.
Travel and airlines
Devices with built in cells travel in hand luggage rather than in the hold, which is the rule for lithium cells generally. Removable batteries should come out for travel so nothing switches on inside a bag. The travel page covers locks, cases and the practical side of getting a drawer through an airport without incident.
Replaceable cells
Objects taking standard cells have one clear advantage: the battery can be replaced when it fails, which is usually the first thing to fail. The drawbacks are weight, a battery compartment that has to be sealed against water, and a slow decline in power as the cells drain rather than the flat output of a regulated rechargeable design.