Batteries, and power in general, is termed a "critical enabling technology". Historically, the subject is poorly managed in MoD. For example, 10 years ago the focus was on providing enough man-portable power to last a 48-hour dismounted mission. MoD let a 3-year R&D contract to produce a prototype, ignoring the fact one bidder produced an old production model that more than met the specification. The winner gave up after 2 years. Faced with that scenario, and as B2N2 says, we are a long way away.
The other determining factor is the old "battlefield fuel" chestnut, whereby our allies try to achieve interoperability, and share resources; despite perpetual failure to agree such strategies. We have international committees up the ying yang who debate this, seemingly taking two steps back every time they meet. We have people in London who monitor use of the word "interoperability" and actively prevent its use in programme titles or plans. Pontius, you chose a hot potato!