Here's the first photos of our ScoreSure Golf Pro device (yes, still in development!) running off a 400mAh 3.7v li-polymer rechargeable battery. We think it looks the business! And of course, using a rechargeable battery (whether eventually a li-po or a li-ion) means lots more possibilities for the enclosure, since we no longer have to worry about battery flaps and making the inside accessible.

Following a discussion on the RobotBrighton Forum, Robot Steve suggested that li-ions are better/safer than li-po batteries. Despite a recent post here extolling the virtues of li-pos, I think he might be onto something: but perhaps not for the reasons he outlined...

After much reading up on li-ion batteries and their variants, it seems that such batteries have a limited shelf-life. Not just a "hanging-around-waiting-to-be-sold" shelf-life (remember, if the battery discharges too much it can become damaged so they need to be used/charged every few months) but also a "use-by" date: typically 18 months - 5 years.
In fact, due to the heavy charge/discharge cycle that laptop batteries go through, many suppliers treat them as consumables now, and I'm thinking along similar lines for the ScoreSure range of devices. So the batteries need to be removeable at some point, not soldered to the PCB via short wires (as was the idea using li-pos).
Because mobile phones are so commonplace, it shouldn't be difficult to get hold of stocks of 3.7v batteries, quite cheaply, in future - and most of these are li-ion, hard-cased batteries, not the lightweight flexible li-pos discussed in recent posts.

When it comes to recharging li-on batteries, eBay is awash with USB phone chargers, for a couple of quid each (less if you buy in bulk) similar to this one.

So while it's going to be interesting to see what turns up in the post over the next few days, there is still plenty of research ongoing, into li-ions as an alternative.

Watch this space....

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.....

That's what's needed - by switching to a lipo battery, the entire device footprint can be almost halved! First thoughts were of a 7.4v lipo (double-cell battery) but the Nokia shield has already proved that a simple dc-to-dc step up converter can do the job where supply voltage is lower than the required voltage.

Charging requirements for lipo (or li-ion polymer) batteries are very specific and charging more than one cell can be quite tricky - particularly because of the need to stay within safety limits during charging.

It would probably be much easier/safer to stick to a single 3.7v battery with integrated USB charging circuit, and use this to power the Score Sure range of devices.
From initial investigations, a single battery would be much simpler to work with.
In fact, a recent email from NuElectronics confirms that they are working on developing this very idea themselves, to allow roboteers to power Arduino boards (which require 5v) from a single 3.7v lipo cell.

Charging circuits for single cells are freely available on the net and use relatively simple and inexpensive components.
At the heart of most chargers is the MCP73861 by Microchip.

More details (and schematics) will be posted here as they become available....