One of the first things anyone starting in sound will find is that changing AA batteries in even the most basic recorders is tedious. When you recorder is buried in a bag it makes the process even more laborious. Most recorders and mixers designed for location use, even your basics like the lowly Zoom H4n, have some kind of DC power input. The most popular connector in the pro market in recent years has been the Hirose four pin connector, with an input of 9V to 18V, which was actually used on the SQN mixers and is a holdover from those days. Other common power connectors include the 4 pin XLR, used on quite a lot of the slightly larger/older kit like Audio Developments mixers, and recently Sound Devices have implemented a TA4 power input on their Scorpio and 8xx series due to the power requirements of running NP-F chargers built into to machines.
Which ever input your recorder has opens up the possibility in connecting up external high capacity batteries like NP-F, NP1 or eSmart and their associated battery distribution systems (BDS), to get your recorder/mixer powered up all day, or at least the majority of the day, on one battery; and even if it does run low, a new battery can be put in in seconds rather than the rigmarole of opening battery bays for AA's...
So let's look a little closer at the options available to us in 2019.
eSmart / SMBus (further Smart Battery reading)
eSmart batteries are the latest development in battery technology on the market. While they currently use typical Lithium rechargeable cells, they also contain a circuit for battery metrics which can be read by a battery distribution, a charger or infact by some of the newer recorders on the market, with Sonosax pushing this feature first (as they have with many recent developments) on the SX-R4+ recorder. They come in a few capacities but the most common are around the 49Wh and 98Wh marks (so you have a maximum capacity battery you can fly with under the 100Wh aviation limit)
The brands that produce them include AudioRoot, Inspired Energy, RRC among a few others including Sound Devices (which probably just a rebrand). They all provide the same power and metrics systems, but the latest Audioroot revision has all of the battery metrics built into a tiny display on the battery itself, which is quite impressive and handy if you only really power a couple of things on a basic power splitter or Y cord, negating requirement for a dedicated power display BDS.
The chargers for these batteries can also be quite expensive, but they are also quite well engineered, so you do often get what you pay for*.
AudioRoot make a range of very nice BDS's for these batteries which have lovely colour displays with full battery telemetry visible at a glance. With the advent of recorders with built in Smart Battery readers these may be a thing that gets phased out over the next few years.
NP1
The NP1 format has been around as long as sound recording on location has been a thing. It was the battery for the old Fostex PD-4, which was a field recording standard throughout the reign of the DAT tape for recording clarity. NP1 has of course moved on with the battery technology over the years and is now available in high capacity Lithium variants up to the same 98Wh and half sizes. Hawkwoods have made some tech improvements over the last couple of years too. Their latest NP1's (NP-98D) use a smart circuit of their own architecture to relay battery data to the screen on their BDS.
The system has been around for a long time and numerous manufacturers make batteries and chargers for the NP1 system at various price points and with various features. The main contenders are Hawkwoods, Swit and IDX (although it seems Swit and IDX haven't updated their range to the highest capacities which kind of rules them out for batteries, though their chargers are probably still good!).
NP-F
The old Sony DVCAM battery, the NP-Fxxx, series come in a huge range of capacities for different applications and, while Sony have moved on to their own new BP-Uxx series, they still provide an excellent value proposition through 3rd party vendors and manufacturers.
Some of the larger varieties of these come in at up to around the 10,000mAh mark, which makes them excellent high capacity batteries (for relatively low draw devices). I add the brackets there for the simple reason that most of the battery plates that allow you to use these with recorders (so that they output 12v) actually have a relatively low load capacity (which I found out to my detriment when trying to power 4 Audio Ltd A10 receivers and my recorder from a single NP-F on a Hawkwoods DV-SQN2S. I think it would be fine for a mainly analogue radio system.)
With that said the highest capacity batteries can be found on Amazon for as little as £30-£40 and they will power a smallish bag rig with two or three analogue dual receivers for pretty much a full day.
The chargers however have been an issue for me. Using high capacity batteries is one thing but charging them seems to be another issue. Most of the cheap Chinese made chargers available currently are quite slow charging. Most seem to be quite under engineered for these capacities. I've had the most luck using old second hand Sony branded chargers, which seem to be more effective. Of course there are also chargers for these style batteries from Hawkwoods and Swit, which are quite a bit more expensive, so when considering the cost of the cheaper batteries are a little bit disproportionate.
Other Powerbank style solutions
A firm favourite among the Zoom F8/F4 user group is the TalentCell Rechargeable battery system. The 11000 mAh model has a lot of users and people rave a bit about them. They conveniently output a regulated 12v, so they are perfect for powering almost anything in a sound bag. In addition to that they also have USB outputs for powering or charging USB powered bits (like Timecode Systems Ultra Sync One or maybe the Sony UWP-D series radios). For just over £100 you can have two batteries that ought to give you far beyond a days use and you only need a USB charger to get them back up to full power once they're on, meaning they can be charged literally anywhere, including in the car between locations just from the 12v car connector.
Notes
*One charger that I will warn anyone off buying is the Audioroot single channel in-line charger (eLC-SMB). It's actually a cheap Chinese laptop battery charger (alibaba pricing between $25 and $60) with a modified output cable. It is a compact and lightweight fast charger, but the connector used between the power brick and the cable is crap, with terrible fit and the charger itself is poorly constructed. Mine turned intermittent and upon inspection there were several weak solder joints inside, which needed fixing, yet despite repairing those the simple fact was that the connector just wasn't making solid contact unless the cable was laid out perfectly flat. The whole thing was also glued inside the housing making field repairs very time consuming if you want to do it without breaking anything.
(I would welcome comment from AudioRoot on this matter if the charger has been updated or changed since I bought mine)