That charger is a .8/3.3amp charger. It will take a long time for that charger to charge up a larger size battery (group 51 and up). For instance our D5100 and larger batteries have an optimal amperage charge rate of 15amps. That charger will charge the batteries, but it will take a long time to charge them up fully.

So Nathan what features should I look for in a charger for a D3400?

AGM compatible (max 14.4V) and around 15amps charge rate. It would be better to charge at 10amps than 25amps though on a single battery. Its better to look for a intellicharger type that will actually go into a float mode and maintain the battery while it is being charged. This way if you had to or wanted to you could leave the battery hooked up to the charger 365 days out of the year and not have to worry about it overcharging the battery.