Li-ion, Li-Po batteries

There has been much discussion about the merits and, worryingly, the dangers of using li-po batteries for providing power for portable devices.
There seems to be some confusion surrounding the safety of "lipo"s versus "lion"s and the general consensus is that lipos are highly volatile, while lions are the "safe" equivalents.

In fact, the opposite appears to be true - lipos are more robust and less likely to be damaged by shock or being dropped (the most likely cause of battery damage in a portable device). Both lipos and lions need careful regulation during charging to avoid overcharging and potentially causing the battery to get hot, burst, or in extreme cases, explode.

It is this fear of explosion that has many people running for cover as soon as lipo batteries are mentioned. Videos exist on the 'net and YouTube showing these types of batteries blowing up apparently due to a tiny variation in charging voltage. This is not really the case: the videos showing battery explosions are (almost) always extreme examples, where the charging voltage/current is deliberately run at a very high rate, to show what is possible if a battery is overcharged.

Lipos have got a bad name for themselves because of these videos - mainly because their flexible outer casing makes them more liable to the spectacular explosion than the lions (which usually are only available in hard cases which are more likely to leak than explode, which doesn't really make for an interesting video on YouTube!)
However, li-pos are built using a later (and it could be argued improved) technology than li-ons. They store more charge for their size/weight and offer improved discharge rates that li-ons. They are popularly used for model aircraft because they are more resistant to damage by shock (for example, an aircraft falling to ground). Yet somehow, they are still seen as the black sheep of the family! Why is this?

Both li-on and li-po batteries can be damaged by under/over voltage.
If the voltage in either a lipo or a lion battery is allowed to fall too low (e.g. below about 3v in a single cell 3.7v battery) then the internals of the battery can be damaged and the battery may not be able to be fully charged in future. Under voltage of the battery does not, however, cause it to explode, leak, catch fire or even get a bit warm.

If the voltage (or charging current) in either li-on and li-po batteries is too great, both can be damaged: the most extreme example being a fire, but the battery has to be seriously abused for this to happen! The maximum voltage is either 4.1v or 4.2v depending on the battery "header" (graphite or coke). Even a voltage difference of 0.1v can cause problems, so care has to be taken....

Should the battery be over-charged, it makes sense that any with a soft, flexible outer case is more likely to swell (and possibly explode) than one with a rigid, hard case. This is where the idea that li-pos are more dangerous that li-ons seems to come from. But given that li-pos are more robust and can cope with being dropped better than li-ons, the li-po battery can be shaped to fit most enclosure designs and provided that the charging circuit can be included in the handheld device (removing the need for the user to handle the battery, to put it into a charger for example) then the case for li-pos seems quite a strong one!

We've a couple on order and in the post, so in a few days, hopefully we can provide an answer based on experience, rather than speculation.....