First, nothing you did caused this. A rechargeable battery that was low when it was put away keeps draining slowly in storage, and after many months of that it can lose capacity, run down very quickly once revived, or in some cases not come back at all.
The one attempt worth making. Leave it on charge for a solid few hours rather than a few minutes, using a cable you know carries data and power, and watch for any flicker at all from the charge indicator or screen. Even a faint light can mean the battery is coming back slowly — leave it charging and check again later.
Before any of that: if the battery is swollen, hot or leaking, stop — do not charge it. Battery and power safety covers what to do instead.
If it stays dead, message us here, or email [email protected], with which device it is, roughly how long it sat unused, and what happens when you plug it in. A battery that was defective from the start is replaced free; one that has simply run down over a long time in storage counts as wear, so where a battery for your model is still available, we send you a quote first and there are no surprise costs — the framework is in Do your kits have a warranty?
This applies to devices with a built-in rechargeable battery. If yours runs on replaceable batteries instead — Chatter 2.0 and the Mars Rover among them — simply fit a fresh set.