Hi RawC
excellent question to ask and such a great idea that you want to share the information with others this is what i like most about forums people always doing there best share and help others.
Let me be very clear so there is no confusion, the current model Ark Pak being sold in the USA model number AP620US is not able to support a LiFePo4 battery types, as i mention in the above post this battery type requires a very specific charging curve that is not available in the current Ark Pak model number AP620US.
we do have a new/upgraded Ark Pak that will soon be available to the USA, it's approx date of availability is looking like mid/late August 2015, the model number of the new Ark Pak will most likely be AP730US (this is to be confirmed) the new model does have the ability to take a LiFePo4 battery type, so if you are keen to get a LiFePo4 battery type then you will have to wait until the new model is available.
in terms of suggestion for battery brand that uses LiFePo4 batteries i have only had access to testing a Fusion LiFePo4 battery model number V-LFP-12-100 a link is below i am not sure if this battery brand is available in the USA.
http://www.fusionagmbatteries.com.a...M/tabid/337/mode/details/pid/713/Default.aspx
if you want to have the ability to use a LiFePo4 battery then you will have to wait for the new upgraded Ark Pak if you do not want this feature then you are able to purchase the current AP620US.
if you have any more questions please ask and it is great to see other forum users sharing there experiences and questions with others.
Regards
Brett from Ark