You don't need to use 3rd party services, keep your posting key safe and under your personal control.
You can use this opensource bot:
https://busy.org/@inertia/drphilrb-voting-bot-gem-update-and-bug-fixes
install on (for example) a raspberry, add/create users list, select a fixed % of vote on every post created from them, enjoy the autovoting.
I'm personally use it on a raspberry pi2 model B, it works like a charm.