https://www.amazon.com/gp/product/B008KEJ1LM
I've had it for 3 years now and it still works 100%, I see there's an updated version.
I trim my full beard once a week in the shower (where this trimmer lives, being splashed everyday). I charge it once a month, so 4 full beard trims per charge is easy.
I like that it's cordless, waterproof and has a high length resolution (0.5mm) which is easily repeatable
I trim my beard at 5.5mm.