I found my DR680 also to eat (new 2700mAh) AA cells way to fast, so I built an external power pack:
This V-mount plate for LED-lights:
and this step-down converter (high switching frequency!):
Open up the plastic of the V-mount, solder the step-down converter inbetween the wires (you will need some extra wire), adjust the voltage to 12V, close the plastic cover (the converter fits easily inside) and...
...yes, the powerplug is just the right one for the DR680! :-)
I have not tested it yet, but a 100Wh V-mount battery should last....for ever. And a short test confirmed, that the Tascam will instantly switch to the internal batterys without stopping to record if you pull the plug (have not testet undervoltage, but should work the same way).
I use a Tekkeon adjustable-voltage battery. It fits in the Portabrace case for the DR680 well and uses the same size charger so I don't need to pack two into my sound case. BTW, it's well worth always having AA batteries in the unit, itself, because this gives you protection against losing a take to a bumped AC cable.
The Tekkeon battery lasts me for 6-8 hours, typically.
Personally I just went with a 12v lead acid battery to power my rig. It is a painless powering option that cost me 20$ plus some minor soldering. Of all the recorders it is the best for me because it can be adapted to bag work so well. It's a great compromise between performance and cost.
@laserdanger you are aware that batteries have different voltages depending on there condition - a new fully charged battery that is rated at 12V can easily have up to 15V or more.
Thats why I only use this electronic DC/DC converters to stabilize the voltage to a set level. As you also need a difference of 2V, it helps against low voltage drop outs too.
I think thats the reason why the V-mount and gold-mount batterys have 14.4V or 14.8V - thats exactly the voltage you need to drive all this 12V-devices with a simple DC/DC converter.
I am aware that new batteries can and will create an excess of the spec'd voltage. From what I observed most who have had problems with this unit were using Tekeon like devices.
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