JSFiddle - React, Tailwind, and code Playground

HTML

total battles for /account/tanks/: <div id="old"></div>
total battles for /tanks/stats/: <div id="new"></div>

JavaScript

var //accountId = 12676647,
    //region = 'ru',
    accountId = 513142011,
    region = 'eu',
    totalNew = 0,
    totalOld = 0;


$.get('http://api.worldoftanks.' + region + '/wot/account/tanks/?application_id=demo&account_id=' + accountId).done(function(oldData) {
    function getOldData(tankId) {
        var result;
        
        $.each(oldData.data[accountId], function(index, oldTankData) {
            if(oldTankData.tank_id === tankId) {
                result = oldTankData.statistics;
                return false;
            }
        });
        
        return result;
    }
    $.get('http://api.worldoftanks.' + region + '/wot/tanks/stats/?application_id=demo&account_id=' + accountId).done(function(newData) {
        console.log(oldData);
        console.log(newData);
        
        $.each(newData.data[accountId], function(index, newTankData) {
            var tankId = newTankData.tank_id,
                oldTankData = getOldData(tankId);
            
            totalNew += newTankData.all.battles;
            if(!oldTankData) {
                console.log('no tank data in /account/tanks/:');
                console.log(newTankData);
            } else {
                totalOld += oldTankData.battles;
                if(newTankData.all.battles !== oldTankData.battles) {
                    console.log('no match battles count:');
                    console.log({
                        tankId: tankId,
                        oldMethod: oldTankData.battles,
                        newMethod: newTankData.all.battles
                    });
                }
            }
        });
        
        console.log('total battles for /account/tanks/:');
        console.log(totalOld);
        $('#old').text(totalOld);
        console.log('total battles for /tanks/stats/:');
        console.log(totalNew);
        $('#new').text(totalNew);
    });
});