Any tips when it comes to battery preservation in the long run?
Standard practices with lithium-ion batteries apply.
There are some practical and some impractical habits. Keep in mind that this is a consumer grade battery with maximum runtime at lowest cost, means longevity was not the purpose when it was built. This means you have the same energy at 5% as if it was 100%, giving you access to all the functions and performance. Typical lifespan is 300-500
cycles (=recharge to 100%).
Impractical:
The ultimate and best thing to do is to keep the cycles at a minimum. Since that kind of destroys the purpose of having a battery on the go and reduces usage of the Steam Deck, this isn't practical. It's not only the raw number of recharge cycles that count, though. Generally, the deeper the discharge, the more impactful on life reducing will be the charge. So you don't want to run out your battery completely.
In
theory, use lower charge voltage. Most chargers (also for smartphones) charge at 4,2V/cell (for safety reason) which gives maximum capacity because that is what counts for most end-consumers. Lower charge voltage and lower capacity is to be found in the industry. This is, also, not practical for this device.
Lowest capacity loss measured is when charged to 75% and discharged to 65%. This reduces utilization tremendously and is hence highly impractical for the Steam Deck.
Practical:
Keep it in a cool environment.
Elevated temperatures, that reduces performance (as in long-time capacity), start at 30°C, but in fact decreasing performance already begin around 25°C.
Modern smartphones and chargers charge dependently on your usage; slow charge (lower temperatures) over night (e.g. my smartphones charges at the speed necessary to have it fully charged when I get up), fast charge (higher temperatures) over the day when it's heavily needed. I don't think the Steam Deck and its charger supports that kind of charging, though.
You
don't need to disconnect the battery/Steam Deck from the charger when it's at 100%. Modern ion batteries
can't be overcharged because charging stops when the battery is full.
Deep cycles will also increase internal resistance which causes temperature increase and voltage drop; increased ion resistance is permanent. So you want to avoid deep cycles;
good cycle range is between 25 and 80%, not recharging when over 50% is even better (except for the small range mentioned under the impractical habits)
.
Keep in mind that recharging earlier increases recharge frequency and hence still "depletes" available recharge cycles until the battery drops capacity. It's not proportional and still helps, though, as charging at 40% battery capacity can prolong the battery life to
twice the cycles (while you charge 1.6 times more often than going from 0-100%).
In general it is nothing you should worry about
too much since this isn't probably a product for a ten year usage cycle. By the time your battery dropped significantly in capacity to the point it becomes unusable without access to the power grid, there's probably the Steam Deck 3 on its way. (depending on how much you use your Steam Deck there's probably even a Steam Deck 4 out before your battery dies completely).
So in short: keep it cool, don't let the battery deplete completely; charge early, preferably before 25%. You can keep it on the power grid.