There was a card from the post office, hidden under the welcome mat at Nerd Towers, saying that they'd been delivered a few days ago. So after a quick trip to the sorting office, they were proudly displayed on one of our workbenches. Here's a photo of the prototype batteries with charge circuits, from Xing at NuElectronics:



The charge circuits include over/under voltage protection, to keep the li-po cells operating within safe limits as well as a step-up converter, to provide a regulated 5v output from the 3.7v cell. As you can see from the photo, they're just being charged up at the minute. As soon as they're ready for use, we'll see how they perform (with our SureScore Golf device). We'll try one with our current device (which includes software-controlled auto-standby after two minutes of inactivity) and one with a modified device with no auto-standby code: this should give us a good idea of the kinds of times we can expect our devices to run for between charges in both "normal" and "continuous" use modes.

Dear Nerds,

I am sending two battery packs (including charge circuit & DC-DC step up to 5.5V) to you today, one has 650mAh 3.7V capacity, the other one has 400mAh, 3.7V capacity. These li-poly batteries are the ones I bought for prototype. For my project in production, I will use 1500mAh 3.7V li-poly battery, which is a little bit bigger - 60mm x 50mm x 5mm .

You can plug in USB mini cable to the USB socket to charge the battery from the PC (the LED will turn on). The data lines are available on the USB socket, you need to be a bit careful of soldering wires onto it. For power up your PIC/eeprom, I'd think you better use a proper LDO regulator - like the AMS1117 - step down 5V to 3V3; because the battery outputs anywhere between 3.6V to 4.2V directly.

Regards,
Xing

Any day now, we should have a conclusion to the debate "lipos - good, bad or ugly?"

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.....