A battery terminal protective cap with the features I missed on other models I found:

• “snap” profile to engage with the positive terminal
• ridge on the nub for the negative terminal to engage with it
• terminals completely enclosed
• relief on the sides to engage the thumb or the nail for ease of removal.

Unfortunately, the standard for this connection is not very clearly defined (or followed). I have had any number of combinations of fit, from the connector either not engaging at all without massive force, to the connector not staying on. There is no defined amount the terminals must protrude from the battery, the top of the terminals can be flush or up to 2mm above the edge, but I measured 3mm on my batteries.  I have gone through more than 10 iterations of the design to make it fit the best I could, but YMMV I guess. You may need a lot of force to put the cap on, and you might break some “fingers” of the snap profile. At least it prints pretty quick and I won't have wasted a lot of your time. But if you manage to get it on without damage, it should work well (for a while at least).